Bump actions/checkout from 4 to 6 (#139)

Author: dependabot[bot]

.github/workflows/pull_request_label.yml

@@ -11,7 +11,7 @@ jobs:
     timeout-minutes: 1
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
       - name: Check for Semantic Version label

.github/workflows/unit_tests.yml

@@ -60,7 +60,7 @@ jobs:
     steps:
       - name: Checkout repository
         if: ${{ matrix.swift.enabled }}
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
           submodules: true