[chore] note broken go v1.19.4 in contributing.md

[tsmethurst]

Description

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This PR just notes in the contributing doc that go v1.19.4 doesn't work properly, and recommends using a lower or higher version (future proof!).

relates to #1249

Checklist

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• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.