vitess: add go1.26 build patch

[stefanb]

• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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Ref:

• Upstream Build fails with Go 1.26 rc1 vitessio/vitess#19087
• Upstream Support Go 1.26 and later with Swiss maps always enabled vitessio/vitess#19088
• go 1.26rc2, [email protected] 1.25.6 (new formula) #258912

[github-actions]

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