misc: more detailed error message in pass from spec

[superlopuh]

This helped me debug some things before.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02% 🎉

Comparison is base (a4a2dcf) 89.62% compared to head (3b1e94b) 89.65%.

❗ Current head 3b1e94b differs from pull request most recent head 483bd9f. Consider uploading reports for the commit 483bd9f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1329      +/-   ##
==========================================
+ Coverage   89.62%   89.65%   +0.02%     
==========================================
  Files         187      191       +4     
  Lines       24616    24871     +255     
  Branches     3699     3752      +53     
==========================================
+ Hits        22063    22297     +234     
- Misses       1967     1982      +15     
- Partials      586      592       +6     

Files Changed	Coverage Δ
tests/test_pass_from_spec.py	93.33% <100.00%> (+0.15%)	⬆️
xdsl/passes.py	92.72% <100.00%> (+0.27%)	⬆️

... and 9 files with indirect coverage changes

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