chore: use actions/checkout@4 everywhere

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

docs/deliver-to-pypi.md

@@ -48,7 +48,7 @@ well as several useful actions. Alongside your existing job(s) that runs cibuild
     name: Make SDist
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0  # Optional, use if you use setuptools_scm
         submodules: true  # Optional, use if you have submodules

docs/setup.md

@@ -181,7 +181,7 @@ To build Linux, Mac, and Windows wheels using GitHub Actions, create a `.github/
             os: [ubuntu-20.04, windows-2019, macos-11]
 
         steps:
-          - uses: actions/checkout@v3
+          - uses: actions/checkout@v4
 
           - name: Build wheels
             run: pipx run cibuildwheel==2.15.0
@@ -213,7 +213,7 @@ To build Linux, Mac, and Windows wheels using GitHub Actions, create a `.github/
             os: [ubuntu-20.04, windows-2019, macos-11]
 
         steps:
-          - uses: actions/checkout@v3
+          - uses: actions/checkout@v4
 
           # Used to host cibuildwheel
           - uses: actions/setup-python@v3