rename git-annex role to git_annex

ansible-lint's role-name rule requires role directory names to match
^[a-z][a-z0-9_]*$ (no dashes). This has been failing CI on master
since 2026-07-07, unrelated to any specific feature change.

Author: ogajduse

roles/git-annex/defaults/main.yml roles/git_annex/defaults/main.ymlroles/git-annex/defaults/main.yml renamed to roles/git_annex/defaults/main.yml

@@ -1,4 +1,4 @@
 ---
 dependencies:
-  - role: git-annex
+  - role: git_annex
   - role: epel_repositories