Small fixes to the auto-upgrade golang tool

[frouioui]

Description

We could see two issues in the previous golang upgrade auto Pull Requests:

• The bootstrap version was 14.2999999.. instead of 14.3. This is because the summing operations of two float can give different results if there are some gaps in the mantissa.
• The bot would re-create the Pull Request on top of the already existing one.

These two issues are now fixed in this PR.

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

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