⚗️ try to use GCC 10

.github/workflows/ubuntu.yml

@@ -8,8 +8,16 @@ jobs:
 
     steps:
     - uses: actions/checkout@v1
+    - name: install_gcc
+      run: |
+           sudo apt update
+           sudo apt install gcc-10 g++-10
+      shell: bash
     - name: cmake
       run: cmake -S . -B build -D CMAKE_BUILD_TYPE=Debug -DJSON_BuildTests=On
+      env:
+        CC:   gcc-10
+        CXX:  g++-10
     - name: build
       run: cmake --build build --parallel 10
     - name: test