Auto merge of #21368 - fabricedesre:bitflags-update, r=jdm

Upgrade bitflags to latest version

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This is a minor update to the `bitflags` crate. That makes syntax like `pub(crate)` work, and I rely on that in a servo embedder.

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- [ ] These changes fix #__ (github issue number if applicable).

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Author: bors-servo