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] <[email protected]>

.github/workflows/ci.yml

@@ -39,7 +39,7 @@ jobs:
           - windows-latest
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Install Rust
       # --no-self-update is necessary because the windows environment cannot self-update rustup.exe.
       run: rustup update stable --no-self-update && rustup default stable
@@ -58,7 +58,7 @@ jobs:
           - windows-latest
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Install Rust
       # --no-self-update is necessary because the windows environment cannot self-update rustup.exe.
       run: rustup update stable --no-self-update && rustup default stable
@@ -151,7 +151,7 @@ jobs:
           - windows-latest
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Cache cargo build and registry
       uses: actions/cache@v4
       with:
@@ -183,7 +183,7 @@ jobs:
           - ubuntu-latest 
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Cache cargo build and registry
         uses: actions/cache@v4
         with:
@@ -211,7 +211,7 @@ jobs:
           - windows-latest
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Cache cargo build and registry
         uses: actions/cache@v4
         with:
@@ -230,7 +230,7 @@ jobs:
   #   name: valgrind
   #   runs-on: ubuntu-latest
   #   steps:
-  #     - uses: actions/checkout@v3
+  #     - uses: actions/checkout@v4
   #     - name: Cache cargo build and registry
   #       uses: actions/cache@v4
   #       with:
@@ -265,7 +265,7 @@ jobs:
     name: docs
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Cache cargo build and registry
         uses: actions/cache@v4
         with:
@@ -298,7 +298,7 @@ jobs:
       - miri
       - docs
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Install latest nightly
         uses: actions-rs/toolchain@v1
         with: