Update "GitHub Actions" Linux runner to 'ubuntu-latest'

Note: ubuntu-20.04 will be phased out soon

.github/workflows/build.yml

@@ -15,7 +15,7 @@ jobs:
     # well on Windows or Mac.  You can convert this to a matrix build if you need
     # cross-platform coverage.
     # See: https://docs.github.com/en/free-pro-team@latest/actions/learn-github-actions/managing-complex-workflows#using-a-build-matrix
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
 
     steps:
     - uses: actions/checkout@v4