[5.2] Fix Dart Sass deprecations

[C-Lodder]

Summary of Changes

lighten() and darken() are global functions in Dart Sass, that were deprecated as of v1.79.0.
This PR replaces them with color.adjust() inside Joomla's SCSS

Note: Bootstrap's own SCSS still uses these functions, and may or may not fix said deprecations in v5, due to the fact they still support node-sass.

Testing Instructions

Code review

[Quy]

I have tested this item ✅ successfully on e22174c

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44129.}

[viocassel]

I have tested this item ✅ successfully on e22174c

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44129.}

[alikon]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44129.}