Improve URL subsitution for custom crates whit CARGO_USE_GIT[HUB|LAB]

[pizzamig]

Summary

While maintaing a rust application, I found a cargo.toml that specifies
the git URL with { git="https://..." }, cargo.mk expects a form like { git = "https://..." }.
This patch improve the regex making the spaces around the '=' optional

Test Plan

Build all the ports using the CARGO_USE_GIT[HUB|LAB]
List of origins found with

grep -Rl ^CARGO_USE_GIT...= | xargs dirname | sort

[tobik]

All ports that are affected by this are tagged with CARGO_USE_GITHUB and CARGO_USE_GITLAB. Assuming those ports all build (or alternatively if you have checked that the contents of Cargo.toml are the same before and after) then this is approved if you remove the superfluous [].

Mk/Uses/cargo.mk

240

Why do you wrap the space in []? [ starts a list of characters but there is only one char in there AFAICT.

[pizzamig]

Remove useless [ ], as suggested by tobik@

[tobik]

Please commit it. Thanks.