Use Ubuntu-provided git-clang-format in CI check

The 14.0.6 version of git-clang-format (which was introduced in
b377779) appears to be incompatible with clang-format-11. The
result was that context lines of the diff got formatted as well, as seen
in
https://github.com/diffblue/cbmc/actions/runs/3141827465/jobs/5104706348.

Using the distribution-provided version of git-clang-format fixes this
problem.

Author: tautschnig

.github/workflows/pull-request-checks.yaml

@@ -611,10 +611,7 @@ jobs:
           DEBIAN_FRONTEND: noninteractive
         run: |
           sudo apt-get update
-          sudo apt-get install --no-install-recommends -yq clang-format-11
-          wget -O git-clang-format https://raw.githubusercontent.com/llvm/llvm-project/llvmorg-14.0.6/clang/tools/clang-format/git-clang-format
-          chmod u+x git-clang-format
-          mv git-clang-format /usr/local/bin
+          sudo apt-get install --no-install-recommends -yq clang-format clang-format-11
       - name: Check updated lines of code match clang-format-11 style
         env:
           BASE_BRANCH: ${{ github.base_ref }}