Check for ExceptionMiddlware removal in starlette.exceptions

[lrafeei]

After Starlette v0.45.0 the import proxy for ExceptionMiddleware was removed from starlette.exceptions (and now only resides in starlette.middleware.exceptions).

This PR adds an additional checker to make sure that, when checking for double instrumentation, the import proxy exists (which is when this particular issue would occur).

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ PYTHON	bandit	1		0	4.49s
✅ PYTHON	black	1	0	0	0.76s
✅ PYTHON	flake8	1		0	0.41s
✅ PYTHON	isort	1	0	0	0.28s
✅ PYTHON	pylint	1		0	2.01s

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.40%. Comparing base (4c06d26) to head (3b5e14e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1282      +/-   ##
==========================================
- Coverage   79.68%   79.40%   -0.28%     
==========================================
  Files         201      201              
  Lines       22174    22174              
  Branches     3519     3519              
==========================================
- Hits        17669    17607      -62     
- Misses       3355     3424      +69     
+ Partials     1150     1143       -7     

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