Bump actions/checkout from 2 to 2.3.4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 2.3.4.
- [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/v2...v2.3.4)

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

.github/workflows/codeql-analysis.yml

@@ -30,7 +30,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v2.3.4
       with:
         # We must fetch at least the immediate parents so that if this is
         # a pull request then we can checkout the head.

.github/workflows/documentation.yml

@@ -19,7 +19,7 @@ jobs:
 
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v2.3.4
         with:
           submodules: 'recursive'
       - uses: ammaraskar/sphinx-action@0.4

.github/workflows/pythonpackage.yml

@@ -18,7 +18,7 @@ jobs:
         python-version: [3.6, 3.7, 3.8, 3.9]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v2.3.4
       with:
         submodules: 'recursive'
     - name: Set up Python ${{ matrix.python-version }}