Update checkout action to v5

Author: mwilliamson

.github/workflows/tests.yml

@@ -12,7 +12,7 @@ jobs:
 
     steps:
 
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v5
 
     - name: Use Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4
@@ -32,7 +32,7 @@ jobs:
 
     steps:
 
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v5
 
     - name: Use Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4