github: run tests on merge queue

Don't run checks on push to main since the tip of the merge queue is the
same.

.github/workflows/check.yml

@@ -1,6 +1,6 @@
 name: Checks
 
-on: [pull_request, push]
+on: [pull_request, merge_group]
 
 permissions:
   contents: read

.github/workflows/generate.yml

@@ -1,6 +1,6 @@
 name: Generate
 
-on: [pull_request, push]
+on: [pull_request, push, merge_group]
 
 jobs:
   generate_documentation:

.github/workflows/test.yml

@@ -1,6 +1,6 @@
 name: Tests
 
-on: [pull_request, push]
+on: [pull_request, merge_group]
 
 jobs:
   test_suite: