fix: adding missing z-index imports (4.x.x backport) (#4040)

* fix: adding missing import in _suite-header.scss

* fix: adding missing z-index import

Author: hectordavis

packages/react/src/components/ComboBox/_combo-box.scss

@@ -1,6 +1,7 @@
 @use '@carbon/react/scss/components/combo-box';
 @use '../../globals/vars' as *;
 @use '../../globals/mixins' as *;
+@use '@carbon/react/scss/utilities/z-index' as *;
 
 .#{$iot-prefix}--combobox {
   display: flex;

packages/react/src/components/SideNav/_side-nav.scss

@@ -8,6 +8,7 @@
 @use '@carbon/react/scss/motion' as *;
 @use '@carbon/react/scss/type' as *;
 @use '@carbon/react/scss/colors' as *;
+@use '@carbon/react/scss/utilities/z-index' as *;
 /////////////////////////////////////////////
 // AI applications dark sidenav theme styles
 ////////////////////////////////////////////

packages/react/src/components/SuiteHeader/_suite-header.scss

@@ -6,6 +6,8 @@
 @use '@carbon/react/scss/type' as *;
 @use '@carbon/react/scss/components/button' as *;
 @use '@carbon/react/scss/utilities/convert';
+@use '@carbon/react/scss/utilities/z-index' as *;
+
 .#{$iot-prefix}--suite-header-profile {
   background-color: $layer-selected-inverse;
   color: $text-inverse; //$inverse-01