fix(docstring): retain doctest arrow prefix

[aaron-ang]

Summary

Closes #2086.

doctest prefix (>>> ) should be retained in Python docstring to preserve syntax highlighting.

Test Plan

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pandas (https://github.com/pandas-dev/pandas)
- ::error file=pandas/core/indexing.py,line=1470,col=9,endLine=1470,endColumn=28,title=Pyrefly bad-override::Class member `_LocIndexer._convert_to_indexer` overrides parent class `_LocationIndexer` in an inconsistent manner%0A  `_LocIndexer._convert_to_indexer` has type `BoundMethod[_LocIndexer, (self: _LocIndexer, key: Unknown, axis: int) -> ndarray[tuple[Any, ...], dtype[signedinteger[_NBitIntP]]] | ndarray[tuple[Any, ...], dtype[Any]] | dict[str, int | integer[Any]] | dict[str, tuple[Unknown, ...]] | dict[str, Unknown] | Unknown]`, which is not assignable to `BoundMethod[_LocIndexer, (self: _LocIndexer, key: Unknown, axis: int) -> Never]`, the type of `_LocationIndexer._convert_to_indexer`
+ ::error file=pandas/core/indexing.py,line=1470,col=9,endLine=1470,endColumn=28,title=Pyrefly bad-override::Class member `_LocIndexer._convert_to_indexer` overrides parent class `_LocationIndexer` in an inconsistent manner%0A  `_LocIndexer._convert_to_indexer` has type `BoundMethod[_LocIndexer, (self: _LocIndexer, key: Unknown, axis: int) -> int | ndarray[tuple[int], dtype[Any]] | ndarray[tuple[Any, ...], dtype[signedinteger[_NBitIntP]]] | ndarray[tuple[Any, ...], dtype[Any]] | slice[int, int, Any] | slice[Any, Any, Any] | dict[str, int | integer[Any]] | dict[str, tuple[Unknown, ...]] | dict[str, Unknown] | Unknown]`, which is not assignable to `BoundMethod[_LocIndexer, (self: _LocIndexer, key: Unknown, axis: int) -> Never]`, the type of `_LocationIndexer._convert_to_indexer`

[stroxler]

Thanks for the bug report and PR! Looks reasonable to me, I'll aim to get a second review and get it merged soon

[meta-codesync]

@stroxler has imported this pull request. If you are a Meta employee, you can view this in D90594592.

[grievejia]

Review automatically exported from Phabricator review in Meta.

[meta-codesync]

@stroxler merged this pull request in 6940e93.