github: Update actions so they don't use deprecated Node.js 20

.github/workflows/tkm.yml

@@ -31,8 +31,8 @@ jobs:
     env:
       TEST: tkm
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/cache@v4
+      - uses: actions/checkout@v6
+      - uses: actions/cache@v5
         with:
           path: ${{ env.CCACHE_DIR }}
           key: ccache-tkm-${{ github.sha }}