Update dependency testfixtures to v8

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
testfixtures	^7.2.2 -> ^8.3.0

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Release Notes

Simplistix/testfixtures (testfixtures)

v8.3.0

Compare Source

• :class:ShouldRaise now supports :class:ExceptionGroup.

• Fixed bug where :func:~testfixtures.comparison.compare_generator did not respect
  strict=True.

• Fixed bug in the type annotations for :class:ShouldRaise and
  :func:~testfixtures.comparison.compare_exception.

• :class:LogCapture will now raise an exception if closed while still installed.
  This can be a source of particularly confusing bugs.

v8.2.0

Compare Source

• The strict option is now correctly respected when :doc:comparing <comparing> nested objects.

• When comparing :class:~datetime.datetime or :class:~datetime.time instances, if the fold
  is the only thing that's different, it's now shown in the output.

• A more detailed exception is now raised when resolving a :doc:replacement <mocking> doesn't give
  what's expected.

• :doc:Replacement <mocking> of methods on instances is now prevented when strict=True.

• An exception is now raised when :doc:mocking <mocking> and the original is not in the
  __dict__ of its containing objects.

v8.1.0

Compare Source

• Fix bug where replacement of methods on subclasses failed when using :meth:Replacer.on_class.

• Implement :ref:strict comparison <compare-datetime> as an option for :class:~datetime.datetime
  and :class:~datetime.time.

v8.0.0

Compare Source

• Retire zope.component helpers.

• Support :class:bytes in :class:popen.MockPopen commands.

• Allow :class:TempDirectory instances to be traversed as :class:~pathlib.Path objects.

• Use the system default encoding where possible in :class:TempDirectory.

• Add :class:TempDirectory option to manage current working directory.

• Allow string class attributes to be replaced with :class:Replacer and friends.

• Fix nasty bug meaning some :meth:~Replacer.on_class and :meth:~Replacer.in_module
  replacements weren't restored.

• Allow an alternative separator to be used for traversal during replacement with
  :class:Replacer and friends.

• Officially support Python 3.12.

• Drop support Python 3.6.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.19%. Comparing base (3d53555) to head (7d48cb0).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2585   +/-   ##
=======================================
  Coverage   90.19%   90.19%           
=======================================
  Files         256      256           
  Lines       15680    15680           
=======================================
+ Hits        14142    14143    +1     
+ Misses       1538     1537    -1     

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