test: fix flaky reactive test

[yanksyoon]

Applicable spec:

Overview

• fix the flaky reactive test
• add debugging logs to queuesize assertion failures

Rationale

Juju Events Changes

Module Changes

Library Changes

Checklist

• The charm style guide was applied.
• The contributing guide was applied.
• The changes are compliant with ISD054 - Managing Charm Complexity
• The documentation for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, complex).
• The changelog is updated with changes that affects the users of the charm.
• The application version number is updated in github-runner-manager/pyproject.toml.

[github-actions]

Test results for commit 1bcacaa

Test coverage for 1bcacaa

Wrote XML report to coverage/coverage.xml

Static code analysis report

Run started:2025-07-31 04:08:28.704894

Test results:
  No issues identified.

Code scanned:
  Total lines of code: 2026
  Total lines skipped (#nosec): 2
  Total potential issues skipped due to specifically being disabled (e.g., #nosec BXXX): 1

Run metrics:
  Total issues (by severity):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
  Total issues (by confidence):
  	Undefined: 0
  	Low: 0
  	Medium: 0
  	High: 0
Files skipped (0):