[AvatarGroup] Fix misalignment with non-default spacing

[sjdemartini]

Closes #29641

The marginLeft style (applied only for custom spacing) should be applied on all but the last element of the group, in order to avoid misalignment of the Avatar children. This makes the non-default spacing (such as spacing="small" or spacing={10}) consistent with the behavior of the default spacing="medium" CSS, which leaves the margin-left as-is for the :last-child.

Before

After

(This demo uses default spacing, then spacing={10}, then spacing={-10}, then spacing="small".)

• I have followed (at least) the PR section of the contributing guide.

[mui-bot]

Details of bundle changes

Generated by 🚫 dangerJS against 9a772af

[danilo-leal]

Seems good to me!

[siriwatknp]

@sjdemartini Thanks for the fix! Your provided image is all clear.

I put a hold on this because it is a breaking change. I think we should try to use the feature flag and be able to merge the breaking change.

[siriwatknp]

👍

[sjdemartini]

@siriwatknp sounds good, thanks! Is there anything I need to do as far as the feature flag, or is that something on your end?

[siriwatknp]

@siriwatknp sounds good, thanks! Is there anything I need to do as far as the feature flag, or is that something on your end?

No worries, it is on our end to work on the feature flag or any approach that would help us merge the breaking change without waiting for the next version to happen.

[siriwatknp]

@siriwatknp sounds good, thanks! Is there anything I need to do as far as the feature flag, or is that something on your end?

We have concluded in our internal meeting that we will merge the breaking changes PR (mostly related to styles change) if it fixes a bug.

So, I am merging this one!