Add milestone and changelog GHA workflows

.github/workflows/check_changelog.yml

@@ -0,0 +1,23 @@
+name: Check PR change log
+
+on:
+  pull_request:
+    types: [opened, synchronize, labeled, unlabeled]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  pull-requests: read
+
+jobs:
+  changelog_checker:
+    name: Check if change log entry is correct
+    runs-on: ubuntu-latest
+    if: github.repository == 'astropy/regions'
+    steps:
+      - uses: scientific-python/action-check-changelogfile@1fc669db9618167166d5a16c10282044f51805c0 # 0.3
+        env:
+          CHANGELOG_FILENAME: CHANGES.rst
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/check_milestone.yml

@@ -0,0 +1,33 @@
+name: Check PR milestone
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize, milestoned, demilestoned]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  pull-requests: read
+
+jobs:
+  # https://stackoverflow.com/questions/69434370/how-can-i-get-the-latest-pr-data-specifically-milestones-when-running-yaml-jobs
+  milestone_checker:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9.0.0
+        if: github.repository == 'astropy/regions'
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const { data } = await github.request("GET /repos/{owner}/{repo}/pulls/{pr}", {
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                pr: context.payload.pull_request.number
+              });
+              if (data.milestone) {
+                core.info(`This pull request has a milestone set: ${data.milestone.title}`);
+              } else {
+                core.setFailed(`A maintainer needs to set the milestone for this pull request.`);
+              }