.github: run test workflows on merge_group

Make sure they work with merge queues.

.github/workflows/dev-checks.yml

@@ -5,6 +5,7 @@ on:
     branches: [ "main" ]
   push:
     branches: [ "main" ]
+  merge_group:
 
 jobs:
   dev-check:

.github/workflows/playwright.yml

@@ -4,6 +4,7 @@ on:
   pull_request:
     types: [opened, reopened, synchronize, labeled, unlabeled]
   workflow_dispatch:
+  merge_group:
 
 jobs:
   playwright-tests:

.github/workflows/pr_best_practices.yml

@@ -6,6 +6,7 @@ on:
     types: [opened, synchronize, reopened, edited]
   issue_comment:
     types: [created]
+  merge_group:
 
 jobs:
   pr-best-practices: