metrics diff error message in --no-scm projects

[karajan1001]

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I am not sure if there is any other scm tools besides git going to be supported.
If so, the error message"only supported for Git repositories" is not proper one,

fix #3605

[karajan1001]

Updated, I found dvc metrics dfif raise this exception after I initialized a git repository.
This was because the dvc configuration do not updated.
And only with cmd dvc config core.no_scm False , it finally be solved.

[efiop]

@karajan1001 Btw, looks like your git email is not added to your github email list. Please go to https://github.com/settings/emails and make sure that your git email (you can see it in git log, not posting it myself so it is not picked up by bots) is added there. That way all of your contributions will be taken into account by github 🙂

[efiop]

Sorry for the delay! Please take a look at a few comments above.

[jorgeorpinel]

Resolved a few items related to the output string.

[karajan1001]

Resolved a few items related to the output string.

Thank you, I will solve other things after work.

[efiop]

Thank you @karajan1001 ! 🎉