Bump github.com/google/go-containerregistry from 0.5.1 to 0.6.0 (#515)

Bumps [github.com/google/go-containerregistry](https://github.com/google/go-containerregistry) from 0.5.1 to 0.6.0.
- [Release notes](https://github.com/google/go-containerregistry/releases)
- [Changelog](https://github.com/google/go-containerregistry/blob/main/.goreleaser.yml)
- [Commits](google/go-containerregistry@v0.5.1...v0.6.0)

---
updated-dependencies:
- dependency-name: github.com/google/go-containerregistry
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

go.mod

@@ -11,7 +11,7 @@ require (
 	github.com/go-openapi/swag v0.19.15
 	github.com/go-piv/piv-go v1.8.0
 	github.com/google/go-cmp v0.5.6
-	github.com/google/go-containerregistry v0.5.1
+	github.com/google/go-containerregistry v0.6.0
 	github.com/google/gofuzz v1.2.0 // indirect
 	github.com/google/trillian v1.3.14-0.20210713114448-df474653733c
 	github.com/in-toto/in-toto-golang v0.2.1-0.20210627200632-886210ae2ab9