hdl._ir: Improve driver-driver conflict message.

[wanda-phi]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 85.87%. Comparing base (a586df8) to head (58d4127).

Files	Patch %	Lines
amaranth/hdl/_ir.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1158      +/-   ##
==========================================
- Coverage   85.89%   85.87%   -0.02%     
==========================================
  Files          43       43              
  Lines        8687     8689       +2     
  Branches     2067     2067              
==========================================
  Hits         7462     7462              
- Misses       1024     1026       +2     
  Partials      201      201              

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