Fix fileMatch for commodore-helm manager

We need to anchor the beginning of the `fileMatch` commodore-helm regex
`class/[^.].ya?ml$` so that we don't accidentally match any files in
golden tests whose name or path contains the fragment `class/`, such as
component-rook-ceph's `rbd-extra-storageclass` test case.

Unfortunately, writing a test for this is tricky because we're
configuring Renovate internals which we can't easily exercise in our
test cases.

src/commodore-helm/index.ts

@@ -28,7 +28,7 @@ interface KapitanHelmDependency extends KapitanDependency {
 
 export const defaultConfig = {
   // match all class files of the component
-  fileMatch: ['class/[^.]+.ya?ml$'],
+  fileMatch: ['^class/[^.]+.ya?ml$'],
 };
 
 export const supportedDatasources = [HelmDatasource.id];