fix: use gnupg instead of gpg package name on Arch Linux

The Arch Linux pacman package for GPG is called 'gnupg', not 'gpg'.
The molecule prepare.yml was trying to install a non-existent 'gpg'
package, causing failures on the archlinux platform.

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ansible/roles/gitea-runner/molecule/common/prepare.yml

@@ -28,7 +28,7 @@
       community.general.pacman:
         name:
           - curl
-          - gpg
+          - gnupg
           - ca-certificates
         state: present
       when: ansible_facts['os_family'] == 'Archlinux'