Merge pull request #3036 from gitgitgadget/tb/ci-run-cocci-with-18.04

ci: pre-emptively fix the "static-analysis" job

Author: dscho

.github/workflows/main.yml

@@ -349,7 +349,7 @@ 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