Update actions/checkout action to v4

| datasource  | package          | from | to |
| ----------- | ---------------- | ---- | -- |
| github-tags | actions/checkout | v3   | v4 |

Author: renovate[bot]

.github/workflows/benchmarks.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"

.github/workflows/coding-standards.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"

.github/workflows/demo-scripts.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"

.github/workflows/mutation-tests.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"

.github/workflows/phpunit.yml

@@ -27,7 +27,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"

.github/workflows/psalm.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"

.github/workflows/release-on-milestone-closed.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v3"
+        uses: "actions/checkout@v4"
 
       - name: "Release"
         uses: "laminas/automatic-releases@v1"