fix: rescue FormulaSpecificationError in Formula.all

[costajohnt]

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• AI was used to generate or assist with generating this PR. Claude Code was used to help investigate the stack trace and implement the fix. All changes were reviewed and verified manually, and the test suite was run locally (brew tests --only formula — all passing).

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What does this PR do?

When a tap formula has no URL, determine_active_spec raises FormulaSpecificationError. Formula.all already rescues FormulaUnavailableError and FormulaUnreadableError to prevent one broken formula from crashing commands like brew search --eval-all --desc, but FormulaSpecificationError was missing from the rescue clause.

This adds FormulaSpecificationError to the rescue so the broken formula is logged as a warning instead of crashing the entire search.

Why should this be included?

A single broken tap formula (with no URL) shouldn't take down brew search --eval-all --desc for the user's entire formula catalog.

Closes #21794

[costajohnt]

Before/After

[MikeMcQuaid]

Thanks @costajohnt!