Replace theme.palette.theme.hint with theme.palette.text.secondary

Signed-off-by: Andre Wanlin <67169551+awanlin@users.noreply.github.com>

.changeset/shaggy-maps-whisper.md

@@ -0,0 +1,6 @@
+---
+'@backstage/core-components': patch
+'@backstage/plugin-api-docs': patch
+---
+
+Replaced usages of `theme.palette.theme.hint` with `theme.palette.text.secondary` as it has been removed in MUI v5

packages/core-components/src/layout/Sidebar/Items.tsx

@@ -677,7 +677,7 @@ const styledScrollbar = (theme: Theme): CreateCSSProperties => ({
     borderRadius: '5px',
   },
   '&::-webkit-scrollbar-thumb': {
-    backgroundColor: theme.palette.text.hint,
+    backgroundColor: theme.palette.text.secondary,
     borderRadius: '5px',
   },
 });

plugins/api-docs/src/components/OpenApiDefinitionWidget/OpenApiDefinition.tsx

@@ -105,7 +105,7 @@ const useStyles = makeStyles(theme => ({
         fontWeight: theme.typography.fontWeightRegular,
       },
       [`& .model-hint`]: {
-        color: theme.palette.text.hint,
+        color: theme.palette.text.secondary,
         backgroundColor: theme.palette.background.paper,
       },
       [`& .opblock-summary-method,