BUG: Change output returned by _LocIndexer._convert_to_indexer to return key with greater resolution value

[wleong1]

Resolution info:

Resolution.RESO_SEC - 3 for seconds
Resolution.RESO_MIN - 4 for minute

Observation:
With the previous code, when the current entry (resolution: 4, entry: '2024-02-24 10:08') has a greater resolution value than the smallest amongst previous entries (in this case resolution: 3, entry: '2024-02-24 10:2:30'), it is shown that the key is said to exist within the list of keys within the Series even though it shouldn't. This does not happen when a smaller or equal resolution value entry is inserted into the Series.

Thought process:
With the previous code, if the current entry's resolution value is greater than the smallest resolution value amongst the previous entries, the _LocIndexer._convert_to_indexer method will only return an empty list (output of the method labels.get_loc(key)), which might be causing entries with larger resolution values not being inserted into the Series correctly.

Potential solution:
I have changed the method _LocIndexer._convert_to_indexer to return the key ('2024-02-24 10:08') instead of an empty list when the resolution value is greater than the smallest resolution value.

• closes BUG: Unexpected behaviour when inserting timestamps into Series #57596
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/v2.2.1.rst file if fixing a bug or adding a new feature.

[mroeschke]

Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.