Clean up GitHub Actions

.github/workflows/check_external_links.yml

@@ -1,7 +1,6 @@
 name: Check Sphinx external links
 on:
   push:
-  pull_request:
   schedule:
     - cron: '0 5 * * 0'  # once every Sunday at midnight ET
   workflow_dispatch:

.github/workflows/codespell.yml

@@ -1,7 +1,6 @@
 name: Codespell
 on:
   push:
-  pull_request:
   workflow_dispatch:
 
 jobs:

.github/workflows/ruff.yml

@@ -1,7 +1,6 @@
 name: Ruff
 on:
   push:
-  pull_request:
   workflow_dispatch:
 
 jobs:

.github/workflows/run_all_tests.yml

@@ -1,7 +1,5 @@
 name: Run all tests
 on:
-  push:
-  pull_request:
   schedule:
     - cron: '0 5 * * 0'  # once every Sunday at midnight ET
   workflow_dispatch:

.github/workflows/run_coverage.yml

@@ -1,7 +1,6 @@
 name: Run code coverage
 on:
   push:
-  pull_request:
   workflow_dispatch:
 
 jobs: