[ButtonGroup] Should not retain divider color when it is disabled and variant is text

[DavidBoyer11]

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

Fixes #36735

[mui-bot]

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[ZeeshanTamboli]

We need to apply a disabled border color using the disabled class as shown below instead of not applying a border color at all.

material-ui/packages/mui-material/src/ButtonGroup/ButtonGroup.js

Lines 140 to 153 in 4fc9750

	...(ownerState.variant === 'contained' &&
	ownerState.orientation === 'horizontal' && {
	borderRight: `1px solid ${(theme.vars || theme).palette.grey[400]}`,
	[`&.${buttonGroupClasses.disabled}`]: {
	borderRight: `1px solid ${(theme.vars || theme).palette.action.disabled}`,
	},
	}),
	...(ownerState.variant === 'contained' &&
	ownerState.orientation === 'vertical' && {
	borderBottom: `1px solid ${(theme.vars || theme).palette.grey[400]}`,
	[`&.${buttonGroupClasses.disabled}`]: {
	borderBottom: `1px solid ${(theme.vars || theme).palette.action.disabled}`,
	},
	}),

The above code snippet is for the contained variant. The same is to be applied for the text variant for both horizontal and vertical orientations.

Also please add visual regression test. You can follow the README instructions on how to add it.

Changes addressed

[ZeeshanTamboli]

I pushed the remaining changes because the issue is opened from a long time. @DavidBoyer11 Thanks for the PR.