Automatically update the latest tag to the HEAD on master.

.github/workflows/update-tag.yaml

@@ -0,0 +1,39 @@
+name: Update latest tag
+
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - '**.go'
+      - 'go.**'
+      - .github/workflows/update-tag.yaml
+
+permissions:
+  contents: write
+
+jobs:
+  update:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Create latest
+        uses: actions/github-script@v7
+        with:
+          script: |
+            # Deletion no-ops if it's not already there.
+            github.rest.git.deleteRef({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              ref: 'tags/latest',
+              sha: context.sha
+            }).catch(err => {
+              # We use create rather than update, because this ensures that the
+              # 'latest' tag is actually pushed to trigger the publication job.
+              github.rest.git.createRef({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                ref: 'refs/tags/latest',
+                sha: context.sha
+              });
+            })
+