chore(deps): update sigstore/cosign-installer digest to 9c520b9 (#935)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| sigstore/cosign-installer | action | digest | `ef6a6b3` -> `9c520b9` |

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.github/workflows/release-please.yaml

@@ -119,7 +119,7 @@ jobs:
             COMMIT=${{ github.sha }}
             DATE=${{ needs.release-please.outputs.date }}
       - name: Install Cosign
-        uses: sigstore/cosign-installer@ef6a6b364bbad08abd36a5f8af60b595d12702f8
+        uses: sigstore/cosign-installer@9c520b997e685cb69e1ac226f7dce8114e8f36df
 
       - name: Sign the image
         run: |