Allow unused_macro_rules in path tests (backport to beta)

[raoulstrackx]

PR #96150 adds a new lint to warn about unused macro rules (arms/matchers). This causes errors in library/std/src/path/tests.rs on the x86_64-fortanix-unknown-sgx platform. This PR fixes compilation errors on that platform by allowing unused macro rules.

This PR is a backport from #97009

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⚠️ Warning ⚠️

• Pull requests are usually filed against the master branch for this repo, but this one is against beta. Please double check that you specified the right target!

[raoulstrackx]

Can this have a review please?

[raoulstrackx]

Pretty please? :)

[est31]

This PR doesn't need a beta backport, due to #97032 having been beta backported in #97631. Eventually the plan is to re-enable the lint, so having an allow in master is good for future changes, but that won't affect the code in beta.

[raoulstrackx]

No longer needed