Bump actions/checkout from 5 to 6 (#339)

Author: dependabot[bot]

.github/workflows/check_links.yml

@@ -28,7 +28,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       # Restore cache
       - name: Restore lychee cache

.github/workflows/update_links.yml

@@ -21,7 +21,7 @@ jobs:
 
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Query Scryfall API and update picURLs
         shell: bash

.github/workflows/update_version.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Get previous version
         id: get_versions