Bump actions/setup-python from 3 to 4 (#65)

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 3 to 4.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](actions/setup-python@v3...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/fortnightly.yml

@@ -47,7 +47,7 @@ jobs:
       with:
         fetch-depth: 0
     - name: Set up Python
-      uses: actions/setup-python@v3
+      uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python }}
     - name: Install Python dependencies

.github/workflows/testing.yml

@@ -46,7 +46,7 @@ jobs:
       with:
         fetch-depth: 0
     - name: Set up Python
-      uses: actions/setup-python@v3
+      uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python }}
     - name: Install Python dependencies
@@ -69,7 +69,7 @@ jobs:
       with:
         fetch-depth: 0
     - name: Set up Python
-      uses: actions/setup-python@v3
+      uses: actions/setup-python@v4
       with:
         python-version: 3.8
     - name: Install Python dependencies