Fix get_json_schema crash on non-string docstring choices (#47072)
The `(choices: ...)` block in a Google-format docstring is parsed with
`json.loads`, so it accepts any JSON values, but `get_json_schema` then called
`.strip()` on every element. This raised `AttributeError: 'int' object has no
attribute 'strip'` for non-string choices such as `(choices: [1, 2, 3])` or
`(choices: [true, false])`, even though the equivalent `Literal[...]` type hint
already supports non-string enums.
Only strip string choices and leave other JSON values (ints, bools, ...) as-is,
and add a regression test.