gitaly: Revert to use `gomodTidy` instead of `gomodTidy1.17`

With cd86529d (Add gomodTidy1.17 to postUpdateOptions for Gitaly, 2022-10-19), we have switched tho postUpdateOptions to use gomodTidy1.17 instead of gomodTidy. Whereas go mod tidy will by default behave as if the -compat flag was set to the version prior to the one indicated by the go directive in the project's go.mod file, with gomodTidy1.17 we explicitly overrode this to drop compatibility with Go 1.16.

This is causing breakage now though as Gitaly has dropped support for Go 1.17. So let's again revert to use gomodTidy so that Go figures out automatically which versions to retain compatibility with. This both decreases our maintenance burden and should unbreak our builds.

Changelog: fixed