fix: use MINISIGN_PASS environment variable for password

[ramonclaudio]

Summary

• Change from piping password to using MINISIGN_PASS env var
• Remove incorrect MINISIGN_ASK_PASS usage
• Simplify find command for attestation signing
• Ensures password-protected keys work correctly in CI

Problem

The workflow was failing with "Wrong password for that key" because minisign wasn't properly receiving the password. The previous attempts to pipe the password or use MINISIGN_ASK_PASS don't work.

Solution

Use the MINISIGN_PASS environment variable which minisign checks for the password when running in non-interactive mode. This is the standard way to provide passwords to minisign in CI environments.

Changes

• Export MINISIGN_PASS environment variable with the password from GitHub secrets
• Remove piping attempts and MINISIGN_ASK_PASS usage
• Simplified the find command for attestation signing

Testing

This fix ensures the publish workflow can properly sign artifacts when using password-protected minisign keys stored in GitHub secrets.