Fix this reference for JavaScript functions (#38725)

js/tests/unit/dropdown.spec.js

@@ -172,7 +172,10 @@ describe('Dropdown', () => {
 
       const popperConfig = dropdown._getPopperConfig()
 
-      expect(getPopperConfig).toHaveBeenCalled()
+      // Ensure that the function was called with the default config.
+      expect(getPopperConfig).toHaveBeenCalledWith(jasmine.objectContaining({
+        placement: jasmine.any(String)
+      }))
       expect(popperConfig.placement).toEqual('left')
     })
   })