Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/gh-pages.yml

@@ -20,7 +20,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@nightly

.github/workflows/test.yml

@@ -14,7 +14,7 @@ jobs:
     name: Check doc
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@nightly
       - run: cargo install cargo-deadlinks
@@ -58,7 +58,7 @@ jobs:
             variant: minimal_versions
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: MSRV
         if: ${{ matrix.variant == 'MSRV' }}
         run: cp Cargo.lock.msrv Cargo.lock
@@ -117,7 +117,7 @@ jobs:
             toolchain: stable
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@master
         with:
@@ -143,7 +143,7 @@ jobs:
   test-miri:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install toolchain
         run: |
           rustup toolchain install nightly --component miri
@@ -163,7 +163,7 @@ jobs:
   test-no-std:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@nightly
         with:
@@ -175,7 +175,7 @@ jobs:
   # test-avr:
   #   runs-on: ubuntu-latest
   #   steps:
-  #     - uses: actions/checkout@v3
+  #     - uses: actions/checkout@v4
   #     - name: Install toolchain
   #       uses: dtolnay/rust-toolchain@nightly
   #       with:
@@ -186,7 +186,7 @@ jobs:
   test-ios:
     runs-on: macos-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install toolchain
         uses: dtolnay/rust-toolchain@nightly
         with: