Fix GPG signature verification with recent versions of GnuPG

What does this MR do?

This merge request fixes the GPG signature verification for commits for recent versions of GnuPG. Currently the most recent versions (2.2.13 and higher tested) have signed commits show up as unverified despite having a correctly registered GPG key. The problem arises because:

GPGME::Crypto.new.verify(signature_text, signed_text: signed_text)

returns a 16 digit fingerprint in older versions of GPG, but a 40 digit fingerprint in newer ones.

Closes #58747 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
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• Style guides
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• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team