fix(module-federation): remove trailing slash from @mui/material/styles shared dependency key

The shared dependency key `@mui/material/styles/` (with trailing slash) caused
module resolution failures because MUI's package.json exports map only defines
`./styles`, not `./styles/`. This resulted in errors like:

  Package subpath './styles/' is not defined by "exports" in
  @mui/material/package.json

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/module-federation-common/src/defaults.ts

@@ -55,7 +55,7 @@ const defaultSharedDependencies = {
   // MUI v5
   // not setting import: false for MUI packages as this
   // will break once Backstage moves to BUI
-  '@mui/material/styles/': {
+  '@mui/material/styles': {
     host: {},
     remote: {},
   },