The ornamental design for a fixingbracket for a rooftop tent, as shown and described.
1. Fixing bracket for a rooftop tent
1.1: Perspective
1.2: Front
1.3: Back
1.4: Left
1.5: Right
1.6: Top
1.7: Bottom
1.8: Reference
The design is a fixing bracket for a rooftop tent and reference is made to the accompanying reproductions showing the design; reference view 1.8forms no part of the claimed design.