tfproviderlint: pin go@1.26

[stefanb]

Ref:

• tfproviderlint crashes under Go 1.27 with package "context" without types bflad/tfproviderlint#345
• go 1.27.0, go@1.26 1.26.7 (new formula) #288803

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• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>?
• Is your test running fine brew test <formula>?
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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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[github-actions]

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