[build] Fix clang-tidy action (#3246)

Manually install python3.8, as actions/setup-python now needs Ubuntu 20.04.

.github/workflows/lint-format.yml

@@ -36,12 +36,8 @@ jobs:
           git fetch --prune --unshallow
           git checkout -b pr
           git branch -f main origin/main
-      - name: Set up Python 3.8
-        uses: actions/setup-python@v2
-        with:
-          python-version: 3.8
       - name: Install clang-format and clang-tidy
-        run: sudo apt-get update -q && sudo apt-get install -y clang-format-10 clang-tidy-10
+        run: sudo apt-get update -q && sudo apt-get install -y clang-format-10 clang-tidy-10 python3.8
       - name: Install wpiformat
         run: pip3 install wpiformat
       - name: Create compile_commands.json