Series.str.repeat zipping operation produces incorrect proxy

https://github.com/apache/beam/pull/13139#discussion_r513684704

This proxy is incorrectly inferred as bool.

```

In [10]: proxy.dtypes
Out[10]:
str object
repeats int64
dtype: object

In [11]: proxy.str.str.repeat(proxy.repeats)
Out[11]:
Series([], Name: str, dtype: bool)

```

The actual operation does produce object though:

```

In [13]: df.str.str.repeat(df.repeats)
Out[13]:
0 AAA
1 B
2 CCCC
3 DDDDD
4
EE
Name: str, dtype: object

```

Currently we work around this by specifying the proxy manually, maybe it can be fixed upstream?

Imported from Jira [BEAM-11155](https://issues.apache.org/jira/browse/BEAM-11155). Original Jira may contain additional context.
Reported by: bhulette.