ci: bump actions/cache from 5 to 6 (#573)

Author: dependabot[bot]

.github/workflows/security-audit.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
       - uses: actions/checkout@v7
       - name: Cache cargo bin
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: ~/.cargo/bin
           key: ${{ runner.os }}-cargo-audit-v0.22.0