ci: fix ubuntu-22.04 workflows

Containers with `ubuntu-22.04` had incompatible `gcc` and `libstdc++`
versions, so we had to remove `gcc-13` and install `gcc-12`. However,
the issue was fixed and `gcc-13` was removed, so our attempt to remove
it by ourselves started to fail. The commit fixes this problem.

Author: drewdzzz

.github/workflows/reusable-testing.yml

@@ -45,14 +45,6 @@ jobs:
         if: inputs.use-valgrind
         run: sudo apt update && sudo apt install -y valgrind
 
-      # https://github.com/actions/runner-images/issues/8659
-      - name: Remove incompatible libstdc++
-        if: ${{ inputs.runs-on == 'ubuntu-22.04' && inputs.cxx-compiler == 'clang++' && inputs.cxx-standard == 20 }}
-        run: |
-          sudo apt remove gcc-13 g++-13 libstdc++-13-dev gcc g++ libstdc++-dev
-          sudo apt autoremove
-          sudo apt install g++-12
-
       - name: Build tntcxx
         uses: ./.github/actions/build-tntcxx
         with: