Bump actions/setup-python from 5 to 6 (#2301) [skip ci]

Author: dependabot[bot]

.github/workflows/create_release_pr.yml

@@ -30,7 +30,7 @@ jobs:
         uses: cylc/release-actions/check-shortlog@v1
 
       - name: Setup Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: '3.x'
 

.github/workflows/main.yml

@@ -28,7 +28,7 @@ jobs:
           cache: yarn
 
       - name: Setup Python
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@v6
         with:
           python-version: '3.x'