Create selftest workflow for GitHub Actions

Add selftest workflow with good and bad job scenarios.

Author: pmh-weio-test

.github/workflows/selftest.yml

@@ -0,0 +1,22 @@
+name: selftest
+on:
+  push:
+  workflow_dispatch:
+jobs:
+  good:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./
+        with:
+          urls: github.com www.github.com
+  bad-must-fail:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - id: c
+        uses: ./
+        continue-on-error: true
+        with:
+          urls: expired.badssl.com wrong.host.badssl.com self-signed.badssl.com
+      - run: test "${{ steps.c.outputs.failed }}" = "1"