GitHub Actions: Lint on push to master

This should store the cache of dependencies that's usable from pull
requests.

Author: kazk

.github/workflows/lint.yml

@@ -1,5 +1,9 @@
 name: Lint
-on: [pull_request]
+on:
+  push:
+    branches:
+      - master
+  pull_request:
 
 jobs:
   lint:
@@ -23,9 +27,11 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-yarn-
       - run: yarn install --frozen-lockfile
-      - run: yarn format
+      - if: ${{ github.event_name == 'pull_request' }}
+        run: yarn format
       - run: yarn lint:text
       - run: yarn lint:format
-      - uses: stefanzweifel/git-auto-commit-action@v4
+      - if: ${{ github.event_name == 'pull_request' }}
+        uses: stefanzweifel/git-auto-commit-action@v4
         with:
           commit_message: Autoformat with Prettier