Mce-operator-bundle: all github actions pinned by mutable tag, not commit sha

A flaw was found in mce-operator-bundle. The build process fetches and executes scripts from a remote repository without performing integrity checks, such as commit pinning or signature verification. This allows a malicious actor with write access to the remote repository to inject and execute arbitrary code during the build. The consequence is a compromised build process, potentially leading to the distribution of malicious software.