Bug 1723031: Associate `perftest-test` command with `python-test` venv r=ahal

The `pytest` dependency is going to be moved from `common` to the
`python-test` environment. Shift all existing `pytest` usages to
the virtualenv accordingly.

Differential Revision: https://phabricator.services.mozilla.com/D126287

python/mozperftest/mozperftest/mach_commands.py

@@ -158,7 +158,12 @@ def run_perftest(command_context, **kwargs):
     print("\nFirefox. Fast For Good.\n")
 
 
-@Command("perftest-test", category="testing", description="Run perftest tests")
+@Command(
+    "perftest-test",
+    category="testing",
+    description="Run perftest tests",
+    virtualenv_name="python-test",
+)
 @CommandArgument(
     "tests", default=None, nargs="*", help="Tests to run. By default will run all"
 )