doc/Makefile: Add dependency on metadata/ltp.json

Link: https://lore.kernel.org/ltp/20250206153435.1602181-2-pvorel@suse.cz/
Fixes: 1bf344a ("doc: add tests catalog page")
Acked-by: Andrea Cervesato <andrea.cervesato@suse.com>
Signed-off-by: Petr Vorel <pvorel@suse.cz>

Author: pevik

doc/Makefile

@@ -1,4 +1,11 @@
-all:
+top_srcdir		?= ..
+
+include $(top_srcdir)/include/mk/env_pre.mk
+
+${abs_top_builddir}/metadata/ltp.json:
+	$(MAKE) -C ${abs_top_builddir}/metadata
+
+all: ${abs_top_builddir}/metadata/ltp.json
 	sphinx-build -b html . html
 
 spelling: