Update README.md and action.yml for v3.15.1

Author: github-actions[bot]

README.md

@@ -51,7 +51,7 @@ jobs:
     steps:
       - uses: actions/[email protected]
       - uses: DeterminateSystems/determinate-nix-action@v3
-      - uses: DeterminateSystems/flakehub-cache-action@v3 # or v3.15.0 to pin to a release
+      - uses: DeterminateSystems/flakehub-cache-action@v3 # or v3.15.1 to pin to a release
       - run: nix build .
 ```
 
@@ -65,7 +65,7 @@ jobs:
 Unlike `DeterminateSystems/magic-nix-cache-action`, we fully support explicit version pinning for maximum consistency.
 This Action is **automatically tagged** for every release, giving you complete control over your CI environment:
 
-📍 Pinning to `DeterminateSystems/[email protected].0` guarantees:
+📍 Pinning to `DeterminateSystems/[email protected].1` guarantees:
 
 - Same `flakehub-cache-action` revision every time
 - Reproducible CI workflows, even years later