Removes the backslash in migrations.list (#27882)

The use of the backslash was causing issues between different versions
of make.

server/Makefile

@@ -809,7 +809,7 @@ help:
 
 migrations-extract:
 	@echo Listing migration files
-	@echo "# Autogenerated file to synchronize migrations sequence in the PR workflow, please do not edit.\n#" > channels/db/migrations/migrations.list
+	@echo "# Autogenerated file to synchronize migrations sequence in the PR workflow, please do not edit." > channels/db/migrations/migrations.list
 	find channels/db/migrations -maxdepth 2 -mindepth 2 | sort >> channels/db/migrations/migrations.list
 
 test-migration:

server/channels/db/migrations/migrations.list

@@ -1,5 +1,4 @@
 # Autogenerated file to synchronize migrations sequence in the PR workflow, please do not edit.
-#
 channels/db/migrations/mysql/000001_create_teams.down.sql
 channels/db/migrations/mysql/000001_create_teams.up.sql
 channels/db/migrations/mysql/000002_create_team_members.down.sql