Generate ext/psych/depend with mkmf --update-depend

The handwritten `$(OBJS): $(HDRS) ...` rule has no autogenerated section, so `tool/sync_default_gems.rb` copies it over the dependencies ruby/ruby keeps in its own tree. Regenerating the file gives sync a section to minimize and drops the `$(hdrdir)` references, which pin the build to the headers of whichever Ruby generated them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: hsbt

ext/psych/depend

@@ -12,6 +12,17 @@ distclean-so::
 	-cd libyaml && $(MAKE) distclean
 	-$(Q)$(RMDIRS) libyaml/* libyaml
 
-$(OBJS): $(HDRS) $(ruby_headers) \
-  $(hdrdir)/ruby/encoding.h \
-  $(hdrdir)/ruby/oniguruma.h
+# AUTOGENERATED DEPENDENCIES START
+psych.o psych_emitter.o psych_emitter_fy.o psych_parser.o psych_parser_fy.o psych_to_ruby.o psych_yaml_tree.o: psych.h
+psych.o psych_emitter.o psych_emitter_fy.o psych_parser.o psych_parser_fy.o psych_to_ruby.o psych_yaml_tree.o: psych_emitter.h
+psych.o psych_emitter.o psych_emitter_fy.o psych_parser.o psych_parser_fy.o psych_to_ruby.o psych_yaml_tree.o: psych_parser.h
+psych.o psych_emitter.o psych_emitter_fy.o psych_parser.o psych_parser_fy.o psych_to_ruby.o psych_yaml_tree.o: psych_to_ruby.h
+psych.o psych_emitter.o psych_emitter_fy.o psych_parser.o psych_parser_fy.o psych_to_ruby.o psych_yaml_tree.o: psych_yaml_tree.h
+psych.o: psych.c
+psych_emitter.o: psych_emitter.c
+psych_emitter_fy.o: psych_emitter_fy.c
+psych_parser.o: psych_parser.c
+psych_parser_fy.o: psych_parser_fy.c
+psych_to_ruby.o: psych_to_ruby.c
+psych_yaml_tree.o: psych_yaml_tree.c
+# AUTOGENERATED DEPENDENCIES END