Python: add explicit typing extensions dep (#12040)

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Turns out there are many dependencies that install typing-extensions,
but we don't install it by default, fixed here.
Closes #12035

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Author: eavanvalkenburg

python/pyproject.toml

@@ -52,6 +52,8 @@ dependencies = [
     "aiortc>=1.9.0",
     # Protobuf
     "protobuf",
+    # explicit typing extensions
+    "typing-extensions>=4.13",
 ]
 
 ### Optional dependencies