firefly: update homepage and checksum for 1.4.0 release

[stefanb]

Ref:

• go 1.27.0, go@1.26 1.26.7 (new formula) #288803

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[daeho-ro]

New rc version is released, stable one will come soon I guess.

• https://github.com/hyperledger-firefly/cli/releases

[EnriqueL8]

Yes we are releasing a stable one soon, aiming for this week

[SMillerDev]

#294306 (comment) just because there's a new release doesn't mean we should treat it as a safe fix. See https://docs.brew.sh/Homebrew-homebrew-core-Maintainer-Guide#retagged-formulae

[EnriqueL8]

See this comment for explanation #294306 (comment)