TST: skip decimal conversion tests on 32-bit
xref #15865

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15922?src=pr&el=h1) Report
> Merging [#15922](https://codecov.io/gh/pandas-dev/pandas/pull/15922?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c1122523ede85340b042b83b629731db8176378f?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/15922/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/15922?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #15922   +/-   ##
=======================================
  Coverage   90.96%   90.96%           
=======================================
  Files         145      145           
  Lines       49557    49557           
=======================================
  Hits        45081    45081           
  Misses       4476     4476
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.73% <ø> (ø)` | :arrow_up: |
| #single | `40.61% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15922?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/tseries/index.py](https://codecov.io/gh/pandas-dev/pandas/pull/15922?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvaW5kZXgucHk=) | `95.33% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/15922?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `91.03% <0%> (+0.34%)` | :arrow_up: |

------

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> **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/15922?src=pr&el=footer). Last update [c112252...f75fabe](https://codecov.io/gh/pandas-dev/pandas/pull/15922?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).