ruby-mini_portile2: update to 2.8.2.

Upstream changes:
https://github.com/flavorjones/mini_portile/blob/v2.8.2/CHANGELOG.md

2.8.2 / 2023-04-30

Fixed

  * Ensure that the source_directory option will work when given a Windows path
    to an autoconf directory. [#126]

2.8.1 / 2022-12-24

Fixed

  * Support applying patches via git apply even when the working directory
    resembles a git directory. [#119] (Thanks, @h0tw1r3!)

(tsutsui)