actions: update to latest provided versions

- checkout@v4: uses default runtime node20 rather than node16, avoiding
      a deprecation warning.
- macos-12: github actions deprecated macos-11 on 2024-06-28 [1]

[1] https://github.blog/changelog/2024-05-20-actions-upcoming-changes-to-github-hosted-macos-runners/#macos-11-deprecation-and-removal

.github/workflows/compile.yml

@@ -38,7 +38,7 @@ jobs:
  run: sudo apt-get install --no-install-recommends
  valgrind autoconf-archive
  - name: Checkout code
- uses: actions/checkout@v3
+ uses: actions/checkout@v4
  - name: Run autoreconf
  run:
  autoreconf -i
@@ -84,10 +84,10 @@ jobs:
  run: test -z "$(git status --porcelain=v1)"
  macOS:
  name: macOS
- runs-on: macOS-11
+ runs-on: macOS-12
  steps:
  - name: Checkout code
- uses: actions/checkout@v3
+ uses: actions/checkout@v4
  - name: Install software
  run: brew install automake
  - name: Run autoreconf

.github/workflows/coverity-scan.yml

@@ -13,7 +13,7 @@ jobs:
  runs-on: ubuntu-20.04
  steps:
  - name: Checkout
- uses: actions/checkout@v3
+ uses: actions/checkout@v4
  - name: Run autoreconf
  run: autoreconf -i
  - name: Configure with the default compiler