fix: updated tx queue bar zIndex to avoid overlaps (#1276)

* fixed MUI theme zIndex for modals to avoid overlaps

* restored the z-Index to the previous value ( z-index: 1) in the transaction Queue

* adjusted Tx queue bar z-index to 1200 to make sure that looks good with the sidebar

src/components/safe-apps/AppFrame/TransactionQueueBar/styles.module.css

@@ -3,7 +3,9 @@
   bottom: 0;
   right: 0;
   width: 100%;
-  z-index: var(--onboard-modal-z-index, var(--modal-z-index));
+
+  /* MUI Drawer z-index default value see: https://mui.com/material-ui/customization/default-theme/?expand-path=$.zIndex */
+  z-index: 1200;
 
   /*this rule is needed to prevent the bar from being expanded outside the screen without scrolling on mobile devices*/
   max-height: 90vh;