chore: [MICROBA-1780] Copy edits (#901)

A partner was not happy with messaging for a course whose
students were in the "earned-not-available" state. This aims to make the
messaging more clear.

src/courseware/course/course-exit/CourseExit.test.jsx

@@ -136,7 +136,7 @@ describe('Course Exit Pages', () => {
         },
       });
       await fetchAndRender(<CourseCelebration />);
-      expect(screen.getByText('Your grade and certificate will be ready soon!')).toBeInTheDocument();
+      expect(screen.getByText('Your grade and certificate status will be available soon.')).toBeInTheDocument();
     });
 
     it('Displays request certificate link', async () => {