cosign clean subcmd: misleading warning about cleaning "referrers" type

[swivelmargarita]

Description
The warning/suggestion when the --type is attestation or signature and we have referrers type is also present for an image, we get this warning "WARNING: image has referrers, consider using --referrer".

But no such option --referrer exists for cosign clean subcommand:

$ COSIGN_PASSWORD='' cosign attest --predicate <(echo '{"a": "b"}') --key cosign.key  --type custom $IMG_TTL 2>/dev/null

$ cosign clean --force --type attestation $IMG_TTL
WARNING: image has referrers, consider using --referrer

$ cosign clean --force --type attestation  --referrer $IMG_TTL
Error: unknown flag: --referrer
error during command execution: unknown flag: --referrer

I think the warning should be WARNING: image has referrers, consider using --type referrer instead. (--type referrer instead of --referrer):

$ cosign clean --force --type referrer $IMG_TTL
Removed ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7@sha256:ea00e606996adf71d5a4b44ea31cf4fa4149dbd010a91d5b091e2fbff8274e33 from ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7:1h
Removed ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7@sha256:1ec624564991564b4bdbec3c2f06d5706337c8fb520b6173adc955e704a10b45 from ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7:1h
Removed ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7@sha256:343bf08c8cc4bfcfd9f2ebbea99075ba1cf8299257715d8eb58f957c5d9626f6 from ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7:1h
Removed ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7@sha256:de4a3c014ea771ea02d618fb51c6704096d1170642bee63ea62678ef43d14d37 from ttl.sh/edee8e54-bb58-47c8-bdd5-99299d91d8f7:1h

Version

$ cosign version
  ______   ______        _______. __    _______ .__   __.
 /      | /  __  \      /       ||  |  /  _____||  \ |  |
|  ,----'|  |  |  |    |   (----`|  | |  |  __  |   \|  |
|  |     |  |  |  |     \   \    |  | |  | |_ | |  . `  |
|  `----.|  `--'  | .----)   |   |  | |  |__| | |  |\   |
 \______| \______/  |_______/    |__|  \______| |__| \__|
cosign: A tool for Container Signing, Verification and Storage in an OCI registry.

GitVersion:    v3.0.7-0.20260601193450-8cedfdeddb69
GitCommit:     8cedfdeddb69594522af4b24ea9102a84fb4c9c4
GitTreeState:  clean
BuildDate:     2026-06-01T19:34:50Z
GoVersion:     go1.26.3-X:nodwarf5
Compiler:      gc
Platform:      linux/amd64

[swivelmargarita]

The corrected warning. The cosign version is the commit from this MR:

$ cosign version
  ______   ______        _______. __    _______ .__   __.
 /      | /  __  \      /       ||  |  /  _____||  \ |  |
|  ,----'|  |  |  |    |   (----`|  | |  |  __  |   \|  |
|  |     |  |  |  |     \   \    |  | |  | |_ | |  . `  |
|  `----.|  `--'  | .----)   |   |  | |  |__| | |  |\   |
 \______| \______/  |_______/    |__|  \______| |__| \__|
cosign: A tool for Container Signing, Verification and Storage in an OCI registry.

GitVersion:    v3.0.7-0.20260602120739-7401fca61d77
GitCommit:     7401fca61d77eff78a79ef18f1960fff1b5475f8
GitTreeState:  clean
BuildDate:     2026-06-02T12:07:39Z
GoVersion:     go1.26.3-X:nodwarf5
Compiler:      gc
Platform:      linux/amd64


$ cosign clean --force --type signature  $IMG_TTL
WARNING: image has referrers, consider using --type referrer

$ cosign clean --force --type attestation $IMG_TTL
WARNING: image has referrers, consider using --type referrer