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/check.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     name: stable / fmt
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install stable
@@ -34,7 +34,7 @@ jobs:
       matrix:
         toolchain: [stable, beta]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install ${{ matrix.toolchain }}
@@ -51,7 +51,7 @@ jobs:
     runs-on: ubuntu-latest
     name: nightly / doc
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install nightly
@@ -64,7 +64,7 @@ jobs:
     runs-on: ubuntu-latest
     name: ubuntu / stable / features
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install stable
@@ -82,7 +82,7 @@ jobs:
         msrv: [1.65.0] # Let-else statements are used in the code
     name: ubuntu / ${{ matrix.msrv }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install ${{ matrix.msrv }}

.github/workflows/scheduled.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     name: ubuntu / nightly
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install nightly
@@ -35,7 +35,7 @@ jobs:
     # Unfortunately, hashFiles only works in if on steps, so we reepeat it.
     # if: hashFiles('Cargo.lock') != ''
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install beta

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
       matrix:
         toolchain: [stable, beta]
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install ${{ matrix.toolchain }}
@@ -33,7 +33,7 @@ jobs:
     runs-on: ubuntu-latest
     name: ubuntu / stable / coverage
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           submodules: true
       - name: Install stable