tts: Run tests in passthru

It was reported multiple times, that tts tests get stuck when many tests
are run in parallel, like during nixpkgs-review runs.

pkgs/tools/audio/tts/default.nix

@@ -1,8 +1,8 @@
 { lib
 , python3
 , fetchFromGitHub
-, fetchpatch
 , espeak-ng
+, tts
 }:
 
 let
@@ -115,6 +115,10 @@ python.pkgs.buildPythonApplication rec {
     )
   '';
 
+  # tests get stuck when run in nixpkgs-review, tested in passthru
+  doCheck = false;
+  passthru.tests.pytest = tts.overridePythonAttrs (_: { doCheck = true; });
+
   nativeCheckInputs = with python.pkgs; [
     espeak-ng
     pytestCheckHook