toxgen: Detect correct sentry-sdk

Sometimes after switching branches, importlib.metadata(sentry-sdk)
would point to the wrong metadata (SDK 2.x instead of 3.x), which
in turn meant toxgen would think the SDK supports different Python
versions than it should.

Author: sentrivana

scripts/populate_tox/populate_tox.py

@@ -10,7 +10,7 @@
 from bisect import bisect_left
 from collections import defaultdict
 from datetime import datetime, timedelta, timezone  # noqa: F401
-from importlib.metadata import metadata
+from importlib.metadata import PackageMetadata, distributions
 from packaging.specifiers import SpecifierSet
 from packaging.version import Version
 from pathlib import Path
@@ -88,6 +88,13 @@
 }
 
 
+def _fetch_sdk_metadata() -> PackageMetadata:
+    (dist,) = distributions(
+        name="sentry-sdk", path=[Path(__file__).parent.parent.parent]
+    )
+    return dist.metadata
+
+
 def fetch_url(url: str) -> Optional[dict]:
     for attempt in range(3):
         pypi_data = requests.get(url)
@@ -583,8 +590,9 @@ def main(fail_on_changes: bool = False) -> None:
         )
 
     global MIN_PYTHON_VERSION, MAX_PYTHON_VERSION
+    meta = _fetch_sdk_metadata()
     sdk_python_versions = _parse_python_versions_from_classifiers(
-        metadata("sentry-sdk").get_all("Classifier")
+        meta.get_all("Classifier")
     )
     MIN_PYTHON_VERSION = sdk_python_versions[0]
     MAX_PYTHON_VERSION = sdk_python_versions[-1]