Upgrade cosign to version v2.6.1 (#720)

Updated cosign installation to version v2.6.1.

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## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The following pins cosign to v2.6.1. 

For more context:
- goreleaser/goreleaser#6195
- #706
## How Has This Been Tested?
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tested? -->

## Breaking Changes
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## Types of changes
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the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
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that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
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Author: rdimitrov

.github/workflows/release.yml

@@ -26,6 +26,8 @@ jobs:
 
       - name: Install cosign
         uses: sigstore/cosign-installer@faadad0cce49287aee09b3a48701e75088a2c6ad
+        with:
+          cosign-release: "v2.6.1"
 
       - name: Install Syft
         uses: anchore/sbom-action/[email protected]
@@ -83,4 +85,4 @@ jobs:
           build-args: |
             VERSION=${{ steps.meta.outputs.version }}
             GIT_COMMIT=${{ github.sha }}
-            BUILD_TIME=${{ steps.build-time.outputs.timestamp }}
+            BUILD_TIME=${{ steps.build-time.outputs.timestamp }}