DEPR: to_native_types, set_value, iteritems, union_many, to_perioddelta
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

IIUC the docbuild problem is 

```
/home/runner/work/pandas/pandas/doc/source/whatsnew/v2.0.0.rst:182: WARNING: Inline interpreted text or phrase reference start-string without end-string.
```

but line 182 in that file a) is not touched by this PR and b) looks fine to me. Thanks @jbrockmendel 