cmake: test integration with old cmake (v3.11.4 2018-03-28)

It was an exercise to run old cmake versions in CI and in the test suite.

It also revealed that 3.7.2 2017-01-13 is too old to consume libssh2 via
`find_package()` due to:
```
CMake Error at bld-libssh2/_pkg/lib/cmake/libssh2/libssh2-config.cmake:35 (add_library):
  add_library cannot create ALIAS target "libssh2::libssh2" because target
  "libssh2::libssh2_shared" is IMPORTED.
Call Stack (most recent call first):
  CMakeLists.txt:27 (find_package)
```
The mitigation for this issue requires 3.11.

Also:
- rename a few existing envs to use the `TEST_` prefix.
- make the `find_package` test provider stage verbose.

Closes #1591

.github/workflows/ci.yml

@@ -58,6 +58,7 @@ jobs:
         shell: ${{ contains(matrix.image, 'windows') && 'msys2 {0}' || 'bash' }}
     env:
       CC: ${{ !contains(matrix.image, 'windows') && 'clang' || '' }}
+      old-cmake-version: 3.11.4
     strategy:
       fail-fast: false
       matrix:
@@ -75,18 +76,33 @@ jobs:
             mingw-w64-x86_64-zlib mingw-w64-x86_64-libgcrypt mingw-w64-x86_64-openssl mingw-w64-x86_64-mbedtls
 
       - name: 'install packages'
-        if: ${{ !contains(matrix.image, 'windows') }}
         run: |
-          if [[ '${{ matrix.image }}' = *'ubuntu'* ]]; then
+          if [[ '${{ matrix.image }}' = *'windows'* ]]; then
+            cd "${HOME}" || exit 1
+            curl --disable --fail --silent --show-error --connect-timeout 15 --max-time 60 --retry 3 --retry-connrefused \
+              --location 'https://github.com/Kitware/CMake/releases/download/v${{ env.old-cmake-version }}/cmake-${{ env.old-cmake-version }}-win64-x64.zip' --output bin.zip
+            unzip -q bin.zip
+            rm -f bin.zip
+            printf '%s' "${HOME}/cmake-${{ env.old-cmake-version }}-win64-x64/bin/cmake.exe" > "${HOME}/old-cmake-path.txt"
+          elif [[ '${{ matrix.image }}' = *'ubuntu'* ]]; then
             sudo rm -f /var/lib/man-db/auto-update
             sudo apt-get -o Dpkg::Use-Pty=0 install libgcrypt-dev libssl-dev libmbedtls-dev libwolfssl-dev
+            cd "${HOME}" || exit 1
+            curl --disable --fail --silent --show-error --connect-timeout 15 --max-time 60 --retry 3 --retry-connrefused \
+              --location https://github.com/Kitware/CMake/releases/download/v${{ env.old-cmake-version }}/cmake-${{ env.old-cmake-version }}-Linux-x86_64.tar.gz | tar -xzf -
+            printf '%s' "$PWD/cmake-${{ env.old-cmake-version }}-Linux-x86_64/bin/cmake" > "${HOME}/old-cmake-path.txt"
           else
             brew install libgcrypt openssl mbedtls wolfssl
+            cd "${HOME}" || exit 1
+            curl --disable --fail --silent --show-error --connect-timeout 15 --max-time 60 --retry 3 --retry-connrefused \
+              --location https://github.com/Kitware/CMake/releases/download/v${{ env.old-cmake-version }}/cmake-${{ env.old-cmake-version }}-Darwin-x86_64.tar.gz | tar -xzf -
+            printf '%s' "$PWD/cmake-${{ env.old-cmake-version }}-Darwin-x86_64/CMake.app/Contents/bin/cmake" > "${HOME}/old-cmake-path.txt"
           fi
 
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
         with:
           persist-credentials: false
+
       - name: 'via FetchContent'
         run: ./tests/cmake/test.sh FetchContent
       - name: 'via add_subdirectory OpenSSL'
@@ -103,6 +119,26 @@ jobs:
         if: ${{ !contains(matrix.image, 'windows') }}  # MSYS2 wolfSSL package not built with the OpenSSL compatibility option
         run: ./tests/cmake/test.sh find_package -DCRYPTO_BACKEND=wolfSSL
 
+      - name: 'via add_subdirectory OpenSSL (old cmake)'
+        run: |
+          export TEST_CMAKE_CONSUMER="$(cat "${HOME}/old-cmake-path.txt")"
+          [[ '${{ matrix.image }}' = *'macos'* ]] && export CFLAGS='-arch arm64'
+          if [[ '${{ matrix.image }}' = *'windows'* ]]; then
+            export TEST_CMAKE_GENERATOR='MSYS Makefiles'
+            export TEST_CMAKE_FLAGS='-DCMAKE_C_COMPILER=x86_64-w64-mingw32-gcc -DOPENSSL_ROOT_DIR=C:/msys64/mingw64'
+          fi
+          ./tests/cmake/test.sh add_subdirectory -DCRYPTO_BACKEND=OpenSSL ${options}
+
+      - name: 'via find_package OpenSSL (old cmake)'
+        run: |
+          export TEST_CMAKE_CONSUMER="$(cat "${HOME}/old-cmake-path.txt")"
+          [[ '${{ matrix.image }}' = *'macos'* ]] && export CFLAGS='-arch arm64'
+          if [[ '${{ matrix.image }}' = *'windows'* ]]; then
+            export TEST_CMAKE_GENERATOR='MSYS Makefiles'
+            export TEST_CMAKE_FLAGS='-DCMAKE_C_COMPILER=x86_64-w64-mingw32-gcc -DOPENSSL_ROOT_DIR=C:/msys64/mingw64'
+          fi
+          ./tests/cmake/test.sh find_package -DCRYPTO_BACKEND=OpenSSL ${options}
+
   build_linux:
     name: 'linux'
     runs-on: ubuntu-latest