Use checkout v4 (#80)

* update to actions/checkout@v4 in workflows

* update to actions/checkout@v4 in examples

Author: memark

.github/workflows/setup-test-workspace/action.yml

@@ -7,7 +7,7 @@ runs:
   using: 'composite'
   steps:
       - name: Checkout the ref-slice fork
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: mgr0dzicki/cargo-semver-action-ref-slice
           ref: ${{ inputs.ref-slice-ref }}

README.md

@@ -27,7 +27,7 @@ semver-checks:
   runs-on: ubuntu-latest
   steps:
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
     - name: Check semver
       uses: obi1kenobi/cargo-semver-checks-action@v2
 ```
@@ -139,7 +139,7 @@ semver:
   runs-on: ubuntu-latest
   steps:
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
     - name: Check semver
       uses: obi1kenobi/cargo-semver-checks-action@v2
       with:
@@ -149,7 +149,7 @@ semver2:
   runs-on: ubuntu-latest
   steps:
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         path: semver
     - name: Check semver
@@ -167,7 +167,7 @@ semver:
       crate: ['api', 'core']
   steps:
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
     - name: Check semver
       uses: obi1kenobi/cargo-semver-checks-action@v2
       with: