github: run tests on push again

We've temporarily disabled the merge queue because our tests often
require retries to go all-green and this isn't possible to do on the
queue, meaning that it's close to impossible to get a PR merged.
Run tests on push so that they run in main when a PR is merged.

This reverts commit 63feab7d86.

.github/workflows/check.yml

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

.github/workflows/generate.yml

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

.github/workflows/test.yml

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