span_range returns unexpected result (missing days) when using frame month

## Issue Description

### Describe the bug, including details regarding any error messages, version, and platform.

Sometimes (based on the start_date/end_date value), some days are missing when splitting a range of dates using `span_range` with `frame=month`

Doc: https://arrow.readthedocs.io/en/latest/api-guide.html#arrow.arrow.Arrow.span_range

Reproduction
```
import arrow
start_date = arrow.get("2023-01-31T00:00:00+02:00")
end_date = arrow.get("2024-08-20T16:08:09.538605+02:00")
[
[start.isoformat(), end.isoformat()]
for start, end in arrow.Arrow.span_range("month", start_date.datetime, end_date.datetime, exact=True)
]
```

### Output
```
[
['2023-01-31T00:00:00+02:00', '2023-02-27T23:59:59.999999+02:00'],
['2023-02-28T00:00:00+02:00', '2023-03-27T23:59:59.999999+02:00'],
['2023-03-31T00:00:00+02:00', '2023-04-29T23:59:59.999999+02:00'], # missing 28th to 30th march
['2023-04-30T00:00:00+02:00', '2023-05-29T23:59:59.999999+02:00'],
['2023-05-31T00:00:00+02:00', '2023-06-29T23:59:59.999999+02:00'],
['2023-06-30T00:00:00+02:00', '2023-07-29T23:59:59.999999+02:00'],
['2023-07-31T00:00:00+02:00', '2023-08-30T23:59:59.999999+02:00'],
['2023-08-31T00:00:00+02:00', '2023-09-29T23:59:59.999999+02:00'],
['2023-09-30T00:00:00+02:00', '2023-10-29T23:59:59.999999+02:00'],
['2023-10-31T00:00:00+02:00', '2023-11-29T23:59:59.999999+02:00'],
['2023-11-30T00:00:00+02:00', '2023-12-29T23:59:59.999999+02:00'],
['2023-12-31T00:00:00+02:00', '2024-01-30T23:59:59.999999+02:00'],
['2024-01-31T00:00:00+02:00', '2024-02-28T23:59:59.999999+02:00'],
['2024-02-29T00:00:00+02:00', '2024-03-28T23:59:59.999999+02:00'],
['2024-03-31T00:00:00+02:00', '2024-04-29T23:59:59.999999+02:00'],
['2024-04-30T00:00:00+02:00', '2024-05-29T23:59:59.999999+02:00'],
['2024-05-31T00:00:00+02:00', '2024-06-29T23:59:59.999999+02:00'],
['2024-06-30T00:00:00+02:00', '2024-07-29T23:59:59.999999+02:00'],
['2024-07-31T00:00:00+02:00', '2024-08-20T16:08:09.538604+02:00'] # missing 30th july
]
```

### Expected result
We should not miss any day from span_range. However, we...
go from `2023-03-27T23:59:59` to `2023-03-31T00:00:00+02:00`, missing 3 days (2nd to 3rd value)
go from `2024-07-29T23:59:59` to `2024-07-31T00:00:00+02:00`, missing 1 day (last value)

Note :
- this issue may not occur with different dates
- this issue does not occur when using `frame=months` instead of `frame=month`
- this issue does not occur when not specifying `exact=True`

I am unsure of the difference between `month` and `months`, but I don't think this is the expected behavior?

## System Info

- 🖥 **OS name and version**: Windows 10.0.19045 (reproduced on MacOS)
- 🐍 **Python version**: 3.9.6 (reproduced on 3.11)
- 🏹 **Arrow version**: 1.3.0

Start with the Arrow.span_range entry point and run the supplied Python reproduction using frame="month" and exact=True. Compare the yielded boundaries with the expected continuous date range, including the differing behavior of "month" versus "months"; done means no days are missing for the reported dates without regressing the other noted cases.

Written by the indexing model from the issue text.