refactor: use the file extension .yml for all yaml files

The role used .yaml while the molecule scenario used .yml, because molecule hard codes molecule.yml and has no
fallback for the other extension. Aligning all files on .yml keeps the extension consistent across the repository
and avoids surprises when a tool only supports one of both spellings.

Co-authored-by: Copilot <copilot@github.com>

README.md

@@ -10,7 +10,7 @@ The role relies on the modules of the collection `community.crypto`. On Archlinu
 is additionally required, because it provides the `pacman` module.
 
 ```bash
-ansible-galaxy collection install -r requirements.yaml
+ansible-galaxy collection install -r requirements.yml
 ```
 
 Facts must be gathered, because the names of the required python packages, the location of the trust store anchor and