Small PR for testing merge queue (#38)

This _mostly_ a dummy PR we can try landing while merge queues are
enabled (and Bors is disabled) to confirm everything works as expected.

I needed to tweak the PR job slightly to emit a dummy "Publish OK" step.
This is a no-op on PRs but still performs the publish when run in the
queue.

Branch protection settings have been updated to no longer restrict
merging to Bors, with these settings:
<img width="772" alt="Screenshot 2023-08-10 at 3 21 59 PM"
src="https://github.com/pulumi/watchutil-rs/assets/848843/bc6ae693-cf96-4a1f-8a05-629c5c880940">

<img width="772" alt="Screenshot 2023-08-10 at 3 19 56 PM"
src="https://github.com/pulumi/watchutil-rs/assets/848843/65d47f85-98e9-4b53-8392-57124bc66454">

After all the checks pass, the merge button looks like this:
<img width="933" alt="Screenshot 2023-08-10 at 3 46 31 PM"
src="https://github.com/pulumi/watchutil-rs/assets/848843/591e15ec-145a-4cf5-a59e-03169994044b">

Merging will enqueue a squashed commit.

.github/workflows/pr-check.yml

@@ -15,3 +15,23 @@ jobs:
   unit-test:
     name: Unit Test
     uses: ./.github/workflows/ci-unit-test.yml
+
+  build-ok:
+    name: Build OK
+    needs: [lint, unit-test]
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo OK
+
+  test-ok:
+    name: Test OK
+    needs: [unit-test]
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo OK
+
+  publish-ok:
+    name: Publish OK
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo "No-op on PRs to satisfy branch checks"