[BE] Fix rule not found error message (#101745)
Prevent error message from becoming of single column of characters
Thanks @clee200 for explaining how it worked before
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### <samp>🤖 Generated by Copilot at fef1e25</samp>
> _`reject_reason` fixed_
> _Syntax error caused trouble_
> _Autumn of bugs ends_
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101745
Approved by: https://github.com/kit1980, https://github.com/osalpekar
