opam source --dev PKG sets color.ui to false

[dbuenzli]

which I personally find undesirable, just let the user config take over.

> opam --version
2.3.0
> opam source --dev cmdliner
> git config --local color.ui
false

[arozovyk]

Related to #4883 and #4884

[dbuenzli]

Note, regarding relationship to #4883. There is likely a distinction to be made between the git clones that opam does for itself and those that it does for me via opam source.

[kit-ty-kate]

opam uses the same code to fetch git repository when using opam source or the other commands.
A distinction between the two was already made in #5888 so doing the same kind of change for avoiding all the git config settings when using opam source should be fairly easy to do.