Fix FTBFS caused by old python-3.9.x on el9

File "/builddir/build/BUILD/chromium-142.0.7444.52/tools/metrics/histograms/extract_histograms.py", line 81, in EnumDict
    type: str | None
TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

File "/builddir/build/BUILD/chromium-142.0.7444.52/tools/metrics/histograms/extract_histograms.py", line 106, in <module>

   ) -> tuple[str | None, ExtractionErrors]:

TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

File "/builddir/build/BUILD/chromium-142.0.7444.52/tools/metrics/histograms/extract_histograms.py", line 643, in <module>

   def _GetObsoleteReason(node: xml.dom.minidom.Element) -> str | None:

TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

diff -up chromium-142.0.7444.52/tools/metrics/histograms/extract_histograms.py.me chromium-142.0.7444.52/tools/metrics/histograms/extract_histograms.py
--- chromium-142.0.7444.52/tools/metrics/histograms/extract_histograms.py.me	2025-10-28 20:14:35.609014587 +0100
+++ chromium-142.0.7444.52/tools/metrics/histograms/extract_histograms.py	2025-10-28 20:30:30.123641508 +0100
@@ -21,6 +21,7 @@ from typing import Any, TypedDict
 import xml.dom.minidom
 
 import histogram_configuration_model
+from typing import Optional, Union
 
 sys.path.append(os.path.join(os.path.dirname(__file__), '..', 'common'))
 import xml_utils
@@ -78,7 +79,7 @@ class EnumDict(TypedDict, total=False):
   """A dict representing an enum."""
 
   name: str
-  type: str | None
+  type: Optional[str]
   buckets: list[_BucketDict]
   summary: str
 
@@ -102,7 +103,7 @@ def ExpandHistogramNameWithSuffixes(
     suffix_name: str,
     histogram_name: str,
     histogram_suffixes_node: xml.dom.minidom.Element,
-) -> tuple[str | None, ExtractionErrors]:
+) -> tuple[Optional[str], ExtractionErrors]:
   """Creates a new histogram name based on a histogram suffix.
 
   Args:
@@ -304,7 +305,7 @@ def _ExtractOwners(node: xml.dom.minidom
 
 def _ExtractImprovementDirection(
     histogram_node: xml.dom.minidom.Element,
-) -> tuple[str | None, ExtractionErrors]:
+) -> tuple[Union[str, None], ExtractionErrors]:
   """Extracts improvement direction from the given histogram element, if any.
 
   Args:
@@ -639,7 +640,7 @@ def ExtractVariantsFromXmlTree(
   return variants_dict, errors
 
 
-def _GetObsoleteReason(node: xml.dom.minidom.Element) -> str | None:
+def _GetObsoleteReason(node: xml.dom.minidom.Element) -> Optional[str]:
   """If the node's histogram is obsolete, returns a string explanation.
 
   Otherwise, returns None.