Fix wrong whitespaces in url tags

• https://edugit.org/AlekSIS/official/AlekSIS-App-Alsijil/-/blob/master/aleksis/apps/alsijil/templates/alsijil/class_register/lesson.html#L28
• https://edugit.org/AlekSIS/official/AlekSIS-App-Alsijil/-/blob/master/aleksis/apps/alsijil/templates/alsijil/class_register/lesson.html#L37

Broken by @ZugBahnHof