properly unmount components between test runs

[schultek]

Description

Resolves #824

Type of Change

• 🛠️ Bug fix

Ready Checklist

• I've read the Contribution Guide.
• In case this PR changes one of the core packages, I've modified the respective CHANGELOG.md file using
  the semantic_changelog format.
• I updated/added relevant documentation (doc comments with ///).
• I added myself to the AUTHORS file (optional, if you want to).

[github-actions]

Package Version Report

The following packages have been updated:
jaspr_test : 0.23.2 -> 0.23.3
jaspr : 0.23.2 -> 0.23.3
jaspr_builder : 0.23.2 -> 0.23.3
jaspr_cli : 0.23.2 -> 0.23.3
jaspr_router : 0.8.3 -> 0.8.4

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.17%. Comparing base (1fa2636) to head (e2c5ae7).

Files with missing lines	Patch %	Lines
packages/jaspr_router/lib/src/router.dart	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #830      +/-   ##
==========================================
+ Coverage   68.98%   69.17%   +0.18%     
==========================================
  Files         212      212              
  Lines       11899    11915      +16     
==========================================
+ Hits         8209     8242      +33     
+ Misses       3690     3673      -17     

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