go/version,internal/gover: treat prerelease patch as valid version

[246859]

go/version.IsValid do not consider prerelease patch as valid version, but some prerelease patches actually do exist in history versions, such as go1.8.5rc5, go1.8.5rc4, go1.9.2rc2 .The version go1.9.2rc2 even could be found from https://go.dev/dl/?mode=json&include=all, and downloaded from https://dl.google.com/go/go1.9.2rc2.linux-amd64.tar.gz. It's unreasonable to treat an existing version as an invalid version, so it should be fixed.

Fixes #68634

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Patch Set 1: Code-Review+1

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Patch Set 1: -Code-Review

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Message from Dmitri Shuralyov:

Patch Set 1:

(1 comment)

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