Bump actions/checkout from 2 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '4'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/docs.yml

@@ -16,7 +16,7 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v2
         with:
           version: '1'

.github/workflows/docscleanup.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout gh-pages branch
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
         with:
           ref: gh-pages
 

.github/workflows/register-pypi.yml

@@ -11,7 +11,7 @@ jobs:
   register:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         ref: ${{ inputs.git_ref }}
     - name: Set up Python

.github/workflows/tests-nightly.yml

@@ -19,7 +19,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-latest]
         jlversion: ['~1.9.0-0', 'nightly']
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ inputs.jl_version }}

.github/workflows/tests.yml

@@ -21,7 +21,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-latest]
         jlversion: ['1','1.6']
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up Julia ${{ matrix.jlversion }}
         uses: julia-actions/setup-julia@v2
         with:
@@ -59,7 +59,7 @@ jobs:
         os: [ubuntu-latest, windows-latest, macos-latest]
         pyversion: ["3.x", "3.8"]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Set up Python ${{ matrix.pyversion }}
         uses: actions/setup-python@v5
         with: