Bump GHA actions

part of matrix-org/synapse#14203

.github/workflows/changelog_check.yml

@@ -6,11 +6,11 @@ jobs:
     if: ${{ github.base_ref == 'main'  || contains(github.base_ref, 'release-') }}
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 0
           ref: ${{github.event.pull_request.head.sha}}
-      - uses: actions/setup-python@v2
+      - uses: actions/setup-python@v4
         with:
           python-version: "3.7"
       - run: python -m pip install towncrier

.github/workflows/docker_check.yml

@@ -36,7 +36,7 @@ jobs:
       # (part of build system config in pyproject.toml) can deduce the package version.
       # See: https://github.com/marketplace/actions/build-and-push-docker-images#path-context
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Build all platforms
         uses: docker/build-push-action@v2

.github/workflows/docker_push.yml

@@ -46,7 +46,7 @@ jobs:
       # (part of build system config in pyproject.toml) can deduce the package version.
       # See: https://github.com/marketplace/actions/build-and-push-docker-images#path-context
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Build and push all platforms
         uses: docker/build-push-action@v2