Align GIT light colored check icon with dark

[beauallison]

I noticed the GIT extension light and dark Check icons were mismatched in size and style; the dark icon looks more consistent with the rest of the VS Code style.

I have replaced the Light Check with the Dark Check and updated the colour to the standard #424242.

References

• Dark Icon
• Light Icon

[bpasero]

@chryw you might want to check on this given your work in #50484

[joaomoreno]

Thanks! 🍻