Fix triggering github actions on pull requests (#193)

Previously, only pull requests from a branch of the repository were
triggering github action workflows.

.github/workflows/Arch.yaml

@@ -1,6 +1,6 @@
 name: pytest-arch
 run-name: Run pytest on Arch Linux
-on: [push]
+on: [push, pull_request]
 jobs:
   pytest:
     runs-on: self-hosted

.github/workflows/GithubRunner.yaml

@@ -1,6 +1,6 @@
 name: pytest-github-runner
 run-name: Run tests for GitHub Runner
-on: [push]
+on: [push, pull_request]
 jobs:
   pytest:
     strategy:

.github/workflows/Ubuntu.yaml

@@ -1,6 +1,6 @@
 name: pytest-ubuntu
 run-name: Run pytest on Ubuntu
-on: [push]
+on: [push, pull_request]
 jobs:
   pytest:
     runs-on: self-hosted

.github/workflows/macOS.yaml

@@ -1,6 +1,6 @@
 name: pytest-macos
 run-name: Run pytest on macOS
-on: [push]
+on: [push, pull_request]
 
 jobs:
   pytest: