[python_basic_gevent] revert Hub value to 2.0e9 — only the regex needed updating

Previous commit dropped the value to 9.0e8 based on a number read from the
captured-profile JSON, which turned out to be a captureProfData subgroup
metric, not the matching-sum the analyzer compares against. The actual
analyzer-side matching sum is ~1.96e9 ns (full ~2s Hub run), matching the
original calibration. Keep the regex fix; restore the original value and
error_margin.

Author: taegyunkim

scenarios/python_basic_gevent/expected_profile.json

@@ -9,8 +9,8 @@
       "stack-content": [
         {
           "regular_expression": "^Hub\\.run;loop\\.run$",
-          "value": 900000000,
-          "error_margin": 30,
+          "value": 2000000000,
+          "error_margin": 25,
           "labels": [
             {
               "key": "task name",