Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build_and_test.yml

@@ -31,7 +31,7 @@ jobs:
             # ubuntu-18.04 does not work due to compile error on asio
             # windows-2019 not included to spare free minutes   
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Prepare dependencies
       run:   |
          if [ "$RUNNER_OS" == "Linux" ]; then

.github/workflows/doxygen-gh-pages.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout 🛎️
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Prepare dependencies
         run: sudo apt-get update && sudo apt-get -yq install libasio-dev doxygen mkdocs graphviz zlib1g-dev gcc clang make cmake python3 python3-pip git openssl libssl-dev
       - name: prepate pip dependencies