git-gui: fix dependency of GITGUI_MAIN on generator

Since 854e883 (git-gui: extract script to generate "git-gui",
2025-03-11), the logic to generate the main script was pulled
out of the Makefile, but adding the resulting generator as a
dependency was missed.

If the logic changes, the main script should be regenerated, so
add it as a dependency.

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>

Author: carenas

Makefile

@@ -168,7 +168,7 @@ git-gui: windows/git-gui.sh
 	cp $< $@
 endif
 
-$(GITGUI_MAIN): git-gui.sh GIT-VERSION-FILE GIT-GUI-BUILD-OPTIONS
+$(GITGUI_MAIN): git-gui.sh GIT-VERSION-FILE GIT-GUI-BUILD-OPTIONS generate-git-gui.sh
 	$(QUIET_GEN)$(SHELL_PATH) generate-git-gui.sh "$<" "$@" ./GIT-GUI-BUILD-OPTIONS ./GIT-VERSION-FILE
 
 XGETTEXT   ?= xgettext