ci: run the required workflows for the merge queue

main no longer requires a branch to be up to date before it merges, so a
PR no longer re-runs CI after every other merge. The Tests, Code Quality
and Viewer.js workflows also run on merge_group, so the merge queue can
test each PR against the latest main once, in order. The tracked
protection record now says strict: false.

.github/branch-protection.json

@@ -1,6 +1,6 @@
 {
   "required_status_checks": {
-    "strict": true,
+    "strict": false,
     "contexts": [
       "py3.12 on ubuntu-latest",
       "py3.13 on ubuntu-latest",

.github/workflows/code-quality.yml

@@ -4,6 +4,7 @@ permissions:
   contents: read
 
 on:
+  merge_group:
   push:
     branches: [main]
   pull_request:

.github/workflows/test.yml

@@ -4,6 +4,7 @@ permissions:
   contents: read
 
 on:
+  merge_group:
   pull_request:
     branches: [main]
   push:

.github/workflows/viewerjs-check.yml

@@ -1,6 +1,7 @@
 name: Viewer.js vendor and compatibility
 
 on:
+  merge_group:
   pull_request:
     branches: [main]
   push: