Bump sigstore/cosign-installer

Bumps [sigstore/cosign-installer](https://github.com/sigstore/cosign-installer) from ef6a6b364bbad08abd36a5f8af60b595d12702f8 to 9c520b997e685cb69e1ac226f7dce8114e8f36df.
- [Release notes](https://github.com/sigstore/cosign-installer/releases)
- [Commits](sigstore/cosign-installer@ef6a6b3...9c520b9)

---
updated-dependencies:
- dependency-name: sigstore/cosign-installer
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build-multiarch.yml

@@ -49,7 +49,7 @@ jobs:
     steps:
       - name: Install cosign
         if: ${{ inputs.sign == true && github.event.release && github.event.action == 'published' }}
-        uses: sigstore/cosign-installer@ef6a6b364bbad08abd36a5f8af60b595d12702f8 #v2.6.0
+        uses: sigstore/cosign-installer@9c520b997e685cb69e1ac226f7dce8114e8f36df #v2.6.0
         with:
           cosign-release: 'v2.0.0'