fix(issue-details): Fix border radius on assignee selector (#76303)

this pr fixes a minor issue with the border radius on the assignee
selector
 before: 
![Screenshot 2024-08-15 at 3 06
38 PM](https://github.com/user-attachments/assets/8a5ea703-1a7f-4cfc-881e-4c025d75c01a)

after: 
![Screenshot 2024-08-15 at 3 06
23 PM](https://github.com/user-attachments/assets/de113171-651e-4a4e-b0e5-dc3ac276af2e)

static/app/components/group/assigneeSelector.tsx

@@ -112,6 +112,6 @@ const StyledDropdownButton = styled(Button)`
   border: none;
   padding: 0;
   height: unset;
-  border-radius: 10px;
+  border-radius: 20px;
   box-shadow: none;
 `;