[R] readr short type mapping has T and t backwards

[asfimport]

ARROW-6537 added the mapping of single-character column types from readr to Arrow types, but it seems that T got mapped to time32() instead of timestamp(); likewise t got mapped wrong.

Reporter: Neal Richardson / @nealrichardson
Assignee: Dragoș Moldovan-Grünfeld / @dragosmg

PRs and other links:

• GitHub Pull Request #11327

_{Note: This issue was originally created as ARROW-13624. Please see the migration documentation for further details.}

[asfimport]

Neal Richardson / @nealrichardson:
Issue resolved by pull request 11327
#11327