BFF: fix proxy url for getting default branch #12479

Job	Run time
Check unpinned dependencies	11s
Test Server	20s
Install everything with PNPM and cache it / Install everything with PNPM and cache it	1m 46s
Run BFF Tests	1m 20s
Deploy Branch Editor	3m 10s
Test Editor PR – TypeScript, ESLint, dependency-cruiser	3m 53s
Test Editor PR – Jest tests	6m 7s
Test Editor Shard 2 / Test Editor PR – Karma tests (Shard 2)	7m 10s
Test Editor Shard 1 / Test Editor PR – Karma tests (Shard 1)	8m 31s
Run Comments Tests	2m 35s
Run System Tests	1m 53s
Run Performance Tests	8m 2s
Run Collaboration Tests	1m 43s
	46m 41s

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