chore(nix): use pytest-cov-stub

This is the Nix-convention to opt-out from coverage measurement during build

Author: vlaci

package.nix

@@ -126,17 +126,13 @@ python3.pkgs.buildPythonApplication {
     with python3.pkgs;
     [
       pytestCheckHook
-      pytest-cov
+      pytest-cov-stub
       versionCheckHook
     ]
     ++ runtimeDeps;
 
   versionCheckProgramArg = "--version";
 
-  pytestFlagsArray = [
-    "--no-cov"
-  ];
-
   passthru = {
     # helpful to easily add these to a nix-shell environment
     inherit runtimeDeps;