FIX: set message crash with long error message

[ZLLentz]

Description

• Fix an issue where the "text is too long" branch of the positioner widget's _set_status_text method would not work if the input was a string. There was an implementation error where we checked the input type but did not fully leverage it.
• Add a test for regression coverage.

Motivation and Context

• Tong ran into an issue today where an exception was being raised for what ended up being a limit error, but since the text for the limit error was very long it ended up triggering this bug.

How Has This Been Tested?

Interactively via hotfix + here via unit test

Where Has This Been Documented?

Adding pre-release notes

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings, including context and API
• New/changed functions and methods are covered in the test suite where possible
• Code has been checked for threading issues (no blocking tasks in GUI thread)
• Test suite passes locally
• Test suite passes on GitHub Actions
• Ran docs/pre-release-notes.sh and created a pre-release documentation page
• Pre-release docs include context, functional descriptions, and contributors as appropriate

[tangkong]

Makes sense to me, just a minor nitpick after I squinted at this classically problematic test suite for a bit

[tangkong]

I had to remind myselfl aoub this no_gc call (from an earlier CI overhaul), but its usage here jives with my recollection of when and where we were applying this

[tangkong]

Do we need to add qtbot as a fixture argument to this test? We give qtbot the motor widget in fixture construction, and it's not used to waitUntil or similar in the test body

[ZLLentz]

I think you're right, this is probably a copy/paste test case no thinking situation

[tangkong]

conda 3.11 passed on a re-run. I know I've recently advocated to not permitting flaky testes but the thought of doing yet another deep dive on this test suite scares me slightly

[ZLLentz]

We'll definitely need to dive into the flakiness at some point... I might go in eventually and try to make tests simpler whenever possible

[tangkong]

LGTM