avoid touch toolchain directive in go.mod

[trim21]

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It's really PITA that how go (go itself, not go manager of renovatebot) handle toolchain directive in go.mod.

When you are using a new go version on go.mod with toolchain, it's very likely go will update the toolchain directive on go get. and it cause renovatebot update a toolchian in go.mod unexpectedly.

Which doesn't actually make sence becuase it's a depType=toolchain instead of expected depType=require

The possible solution are:

1. Use same version go version with toolchain directive in go.mod when it has one instead of using go directive

renovate/lib/modules/manager/gomod/artifacts.ts

Line 454 in 72a5af8

const re = regEx(/^go\s*(?<gover>\d+\.\d+)$/m);

2. replace current go get ./... command with go get ./... toolchain@${current toolchain} version so go wont't change it.

For example: