ci: allow the test workflow to be dispatched manually

Author: 0xAHA

.github/workflows/tests.yaml

@@ -5,6 +5,9 @@ on:
     branches: [main]
   pull_request:
     branches: [main]
+  # Lets the suite be run by hand against any branch — used to confirm a test
+  # actually fails when the defect it targets is reintroduced.
+  workflow_dispatch:
 
 jobs:
   # Fast suite: pure protocol logic, no Home Assistant. Runs in well under a second,