fix: improve Go version detection inside workspace

[ldez]

Fixes #4894

To reproduce

#!/bin/bash -e

rm -rf wpsample

mkdir wpsample
cd wpsample

go work init

mkdir a b
echo module a > a/go.mod
echo go 1.20 >> a/go.mod

echo module b > b/go.mod
echo go 1.22 >> b/go.mod

echo package main > b/main.go

go work use a
go work use b

cd b

golangci-lint run --enable=copyloopvar,intrange

Note

By adding golang.org/x/mod as a dependency, a bug inside the integration test for gomodguard has been detected.
The test used the go.mod of golangci-lint instead of a dedicated go.mod so we never saw the problem.
The module defined inside the allowed section was not a module but a package (golang.org/x/mod/modfile) and as the go.mod of golangci-lint didn't contain golang.org/x/mod the problem was hidden.
So I fixed the test because without that, the CI was unhappy with this PR.