chore(ci): bump actions/checkout from 4.3.1 to 6.0.2

Update all workflow files to use actions/checkout v6.0.2 (commit
de0fac2e4500dabe0009e67214ff5f5447ce83dd).

Closes #3

Author: geekmuse

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
       # Stage 1 — PHP syntax check
       # Uses kanboard/kanboard image with entrypoint override (default entrypoint

.github/workflows/codeql.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
       - name: Initialize CodeQL
         uses: github/codeql-action/init@c10b8064de6f491fea524254123dbe5e09572f13  # v4.35.1

.github/workflows/release.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5  # v4.3.1
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd  # v6.0.2
 
       - name: Extract version from tag
         id: version