Bump actions/checkout from 2 to 4 (#63)

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-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/rust.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1
@@ -50,7 +50,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1
@@ -74,7 +74,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1
@@ -98,7 +98,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1
@@ -118,7 +118,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1
@@ -159,7 +159,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1
@@ -183,7 +183,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v2
+        uses: actions/checkout@v4
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1