Update GitHub Actions to Node 24 compatible versions (#100)

GitHub is deprecating Node 20 on Actions runners (EOL April 2026).
Updated actions to their latest major versions with Node 24 support:
- actions/checkout v4 → v6
- actions/cache v3 → v5

Author: Denis-Averin

.github/workflows/check-badges.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Check badges in README.md
       run: ./scripts/check-badges.bash "README.md"

.github/workflows/php-versions.yml

@@ -11,14 +11,14 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Validate composer.json and composer.lock
       run: composer validate
 
     - name: Cache Composer packages
       id: composer-cache
-      uses: actions/cache@v3
+      uses: actions/cache@v5
       with:
         path: vendor
         key: ${{ runner.os }}-php-${{ hashFiles('**/composer.lock') }}
@@ -50,7 +50,7 @@ jobs:
     name: PHP ${{ matrix.php-versions }} Test on ${{ matrix.operating-system }}
     steps:
     - name: Checkout
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
     - name: Install PHP
       uses: shivammathur/setup-php@v2
       with: