tools: ynl: tests: fix leading space on Makefile target

tools: ynl: tests: fix leading space on Makefile target

The ../generated/protos.a rule had a spurious leading space before the
target name. In make, target rules must start at column 0; only recipe
lines are indented with a tab. The extra space caused make to misparse
the rule.

Remove the leading space to match the style of the adjacent
../lib/ynl.a rule.

Fixes: e0aa0c61758f ("tools: ynl: move samples to tests")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Link: https://patch.msgid.link/20260408-ynl_makefile-v1-1-f9624acc2ad9@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>