CI: pin moto to 1.3.4
xref https://github.com/pandas-dev/pandas/issues/22934

Looking back at the logs, moto 1.3.4 didn't seem to have an issues. Going to run this on the CI a few times to see if we get any failures. May have to make some additional pins of boto if this doesn't work.
So far we're 3/3 passing with this pin. If it passes 5 times, I'll go ahead and merge this.

4/4. will this resolve the issue #22934 ?
 That's the hope. We'll leave #22934 open to remind us to remove the pin when it's no longer necessary. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22959?src=pr&el=h1) Report
> Merging [#22959](https://codecov.io/gh/pandas-dev/pandas/pull/22959?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b0f9a104f323d687a56ea878ff78ff005f37b42d?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22959/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22959?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22959   +/-   ##
=======================================
  Coverage   92.18%   92.18%           
=======================================
  Files         169      169           
  Lines       50833    50833           
=======================================
  Hits        46862    46862           
  Misses       3971     3971
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.6% <ø> (ø)` | :arrow_up: |
| #single | `42.36% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22959?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22959?src=pr&el=footer). Last update [b0f9a10...f4cf3dd](https://codecov.io/gh/pandas-dev/pandas/pull/22959?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Ok, that's 5/5... Going to merge.