Plugins: Remove unnecessary error result from env vars interface (#73224)

* remove error from interface

* fix test

pkg/plugins/manager/pipeline/initialization/steps_test.go

@@ -124,9 +124,9 @@ type fakeEnvVarsProvider struct {
 	GetFunc func(ctx context.Context, p *plugins.Plugin) []string
 }
 
-func (f *fakeEnvVarsProvider) Get(ctx context.Context, p *plugins.Plugin) ([]string, error) {
+func (f *fakeEnvVarsProvider) Get(ctx context.Context, p *plugins.Plugin) []string {
 	if f.GetFunc != nil {
-		return f.GetFunc(ctx, p), nil
+		return f.GetFunc(ctx, p)
 	}
-	return nil, nil
+	return nil
 }