Fix a lot of linting issues

After we introduced the linter we haven't really touched the old code.
This commit now fixes all linting issue that exist right now.

api/api_test.go

@@ -56,7 +56,8 @@ func TestNewRouterV1WithAuthenticationEnabled(t *testing.T) {
 	})
 
 	t.Run("protected route is not accessible", func(t *testing.T) {
-		// request an available API route that should be guarded by authentication (which one, in particular, does not matter here)
+		// request an available API route that should be guarded by authentication.
+		// (which one, in particular, does not matter here)
 		request, err := http.NewRequest(http.MethodPost, "/api/v1/runners", nil)
 		if err != nil {
 			t.Fatal(err)