ci/GHA: disable trap-caching in CodeQL

To avoid littering the Actions cache.

Another, libssh2-specific issue is that the cache is bound to codeql
version, master commit hash and platform. But in libssh2 we buidl 4
different configurations on Linux, which caused these caching failures:
```
C (OpenSSL) Failed to save: Unable to reserve cache with key codeql-trap-1-2.23.0-cpp-5bd1baed82ada192a2ae7e9801882813853e4d87, another job may be creating this cache.
C (wolfSSL) Failed to save: Unable to reserve cache with key codeql-trap-1-2.23.0-cpp-5bd1baed82ada192a2ae7e9801882813853e4d87, another job may be creating this cache.
C (mbedTLS) Failed to save: Unable to reserve cache with key codeql-trap-1-2.23.0-cpp-5bd1baed82ada192a2ae7e9801882813853e4d87, another job may be creating this cache.
```
Ref: https://github.com/libssh2/libssh2/actions/runs/17744827522

It's probably something to fix, because it suggests that it's unexpected
to build multiple configs in a matrix. Perhaps it's better to build them
after each other in the build step. Though it's not yet clear how
the CodeQL engine is considering coverage for different build
configurations of the same codebase.

Ref: https://github.com/curl/curl/pull/18613
Ref: 9618c337d1

.github/workflows/codeql.yml

@@ -75,6 +75,7 @@ jobs:
         with:
           languages: cpp
           build-mode: manual
+          trap-caching: false
 
       - name: 'build'
         timeout-minutes: 5