fix(ci): remove gpg sign command override, let rpm-sequoia sign natively

Fedora 43 uses rpm-sequoia which does not expand %{__plaintext_filename}
or %{__signature_filename} from %__gpg_sign_cmd. Remove the override
and let rpm-sequoia read the gpg key directly. The key trust and
gpg-agent loopback config are already in place.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

rpm/rpmmacros

@@ -1,2 +1 @@
 %_gpg_name @GPG_NAME@
-%__gpg_sign_cmd %{__gpg} --batch --verbose --no-armor --pinentry-mode loopback --passphrase '' --no-secmem-warning -u "%{_gpg_name}" -sbo %{__signature_filename} -- %{__plaintext_filename}