Upgrade self-tests to deal with github.com/oras-project/oras-go v2.6.2 security release: FAIL: TestPushSignature

[jas4711]

Is your feature request related to a problem?

Hi! This project uses oras-go 2.6.0 and recently v2.6.2 was released which fixes several security bugs. However upgrading it leads to build failures in notation-go. Could you look into this? I help maintain this package for Debian, and to allow the security release to migrate, I'm going to disable these self tests -- but I prefer a proper fix.

Probably related to #585

https://salsa.debian.org/jas/golang-oras-oras-go/-/jobs/10025571#L1790

=== RUN   TestPushSignature
=== RUN   TestPushSignature/failed_to_upload_signature
=== RUN   TestPushSignature/successfully_uploaded_signature_manifest
    repository_test.go:421: error = blob upload Location "" is on a different host than the registry "localhost:5000", expectErr = false
--- FAIL: TestPushSignature (0.00s)
    --- PASS: TestPushSignature/failed_to_upload_signature (0.00s)
    --- FAIL: TestPushSignature/successfully_uploaded_signature_manifest (0.00s)
=== RUN   TestPushSignatureImageManifest
    repository_test.go:439: failed to push signature
--- FAIL: TestPushSignatureImageManifest (0.00s)

/Simon

What solution do you propose?

Fix tests

What alternatives have you considered?

Disabling tests

Any additional context?

Using notation-go v1.3.2