Change startMinutes to startHours

[MatthiasReumann]

Motivation and Context

Introduced in #1125.

Steps for Testing

Prerequisites:

• 1 Admin
• 1 Course

1. Log in
2. Navigate to a Admin Course Page
3. Try to insert invalid start hours, minutes, and seconds. (e.g. startMinutes=107)
4. The "Add" button should be disabled.

[github-actions]

Your Testserver will be ready at https://1127.test.live.mm.rbg.tum.de in a few minutes.

Logins

Kurs1	Kurs2	Kurs3	Kurs4
public	public	loggedin	enrolled
prof1	prof1	prof2	prof1 prof2
student1 student2 student3	student1 student2	student2 student3	student1 student2

[joschahenningsen]

Good catch!