Merge branch 'tb/ci-run-cocci-with-18.04'

The version of Ubuntu Linux used by default at GitHub Actions CI
has been updated to one that lack coccinelle; until it gets fixed,
work it around by sticking to the previous release (18.04).

* tb/ci-run-cocci-with-18.04:
  .github/workflows/main.yml: run static-analysis on bionic

Author: gitster

.github/workflows/main.yml

@@ -340,7 +340,7 @@ jobs:
     if: needs.ci-config.outputs.enabled == 'yes'
     env:
       jobname: StaticAnalysis
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     steps:
     - uses: actions/checkout@v1
     - run: ci/install-dependencies.sh