Fix missing reset in isolation function

[Tyl13]

Adds missing _compat.should_strip_ansi reset back to the original version of the function.

fixes #2732

• [x] Add tests that demonstrate the correct behavior of the change. Tests should fail without the change.
• [x] Add or update relevant docs, in the docs folder and in code.
• [x] Add an entry in CHANGES.rst summarizing the change and linking to the issue.
• [x] Add .. versionchanged:: entries in any relevant code docs.