[BUG] `git clone '-c KEY=VALUE'` no longer works

Hi,

There's a small regression in Git v2.52.0; it used to be that a command of the form

    git clone '-c KEY=VALUE' ...

or

    git clone '--config= KEY=VALUE' ...

would trim whitespace around KEY, making the command equivalent to this:

    git clone --config=KEY=VALUE ...

The relevant code was here: https://github.com/git/git/blob/v2.51.2/config.c#L649

That functionality was removed in this refactoring commit: https://github.com/git/git/commit/dcecac2580ef871186fdc4e9efc87815a4ce4c66

As a result, a command like the above will now fail, with an error such as this:

    error: invalid key:  advice.detachedHead=false
    fatal: unable to write parameters to config file

because config keys are not allowed to contain whitespace.

I believe this change was unintentional; it was not mentioned in the commit message or the release notes.

This probably isn't a common case, and the project where I ran into this issue has already fixed it on their end (they now pass -c and KEY=VALUE as separate arguments); but since Git aims to ensure backward-compatibility where possible, I figured I should report it.

Thanks in advance! -Ran