Update GitHub workflow configurations

Update actions to run on pull requests as well as main.
Update the actions to their latest versions.
Skip the dev environment setup as it isn't currently needed.

.github/workflows/ci.yml

@@ -1,6 +1,10 @@
 name: Python package
 
-on: [push]
+on: 
+  push:
+  pull_request:
+    branches:
+      - main
 
 jobs:
   build:
@@ -11,14 +15,10 @@ jobs:
         python-version: [3.8, 3.12]
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v1
+      uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        python -m pip install -e .[dev]
     - name: Run tests
       run: python run tests