Bump deps/curl from `b4d73e6` to `b9c2a56`

[dependabot[bot]]

Bumps deps/curl from b4d73e6 to b9c2a56.

Commits

• b9c2a56 managen: warn on excessively long help texts
• 72abf7c lib: tidy up types and casts
• ad837e9 cmdline-opts/ech.md: shorten the help text
• 5bfd0cd cmdline-opts/_PROTOCOLS.md: mention WS(S)
• dfbf2b7 GHA: disable TFTP and WebSockets tests in old-mingw-w64
• 5e2e470 cmdline-opts/fail.md: expand and clarify
• 881e9a6 doh-insecure.md: expand
• 65651dc cmdline: expand proxy option explanations
• 6ceb23d cmdline-opts: expand the parallel explanations
• 4a25812 RELEASE-NOTES: synced
• Additional commits viewable in compare view

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