Use @pytest.mark.flaky decorator instead of @flaky.flaky (#4700)

Use the modern `@pytest.mark.flaky` decorator over `@flaky.flaky` in tests.
This avoids typing issues, and makes the tests compatible with other
implementations of that decorator, such as `pytest-rerunfailures`.

Signed-off-by: Michał Górny <mgorny@gentoo.org>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>

Author: mgorny

opentelemetry-sdk/tests/metrics/test_periodic_exporting_metric_reader.py

@@ -22,7 +22,7 @@
 from typing import Optional, Sequence
 from unittest.mock import Mock
 
-from flaky import flaky
+import pytest
 
 from opentelemetry.sdk.metrics import Counter, MetricsTimeoutError
 from opentelemetry.sdk.metrics._internal import _Counter
@@ -194,7 +194,7 @@ def test_ticker_value_exception_on_negative(self):
             export_interval_millis=-100,
         )
 
-    @flaky(max_runs=3, min_passes=1)
+    @pytest.mark.flaky(max_runs=3, min_passes=1)
     def test_ticker_collects_metrics(self):
         exporter = FakeMetricsExporter()