Bump actions/setup-python from 4 to 6

Bumps [actions/setup-python](https://github.com/actions/setup-python) from 4 to 6.
- [Release notes](https://github.com/actions/setup-python/releases)
- [Commits](actions/setup-python@v4...v6)

---
updated-dependencies:
- dependency-name: actions/setup-python
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/testing.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
-      - uses: actions/setup-python@v4
+      - uses: actions/setup-python@v6
         with:
           python-version: '3.13'
           cache: pip
@@ -67,7 +67,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
-      - uses: actions/setup-python@v4
+      - uses: actions/setup-python@v6
         with:
           python-version: ${{ matrix.config.python }}
           cache: pip
@@ -123,7 +123,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
-      - uses: actions/setup-python@v4
+      - uses: actions/setup-python@v6
         with:
           python-version: '3.13'
           cache: pip