Fix race condition between linking ruby and update-default-gemspecs

`yes-update-default-gemspecs` uses `$(XRUBY)` which execs the ruby
binary, but only depended on `main` (extensions and encodings).
When `make runirb` runs with parallel jobs, the linker may still be
writing the ruby binary while `update-default-gemspecs` tries to
exec it, causing `Errno::EACCES` (Permission denied).

Add `$(PROGRAM)` as a dependency so the binary is fully linked
before attempting to execute it.

This is to prevent CI from randomly failing on the runirb step, e.g.
https://github.com/ruby/ruby/actions/runs/23921136182/job/69767485157?pr=16648

Author: k0kubun

common.mk

@@ -1578,7 +1578,7 @@ no-test-bundled-gems-precheck:
 
 update-default-gemspecs: $(TEST_RUNNABLE)-update-default-gemspecs
 no-update-default-gemspecs:
-yes-update-default-gemspecs: $(PRECHECK_BUNDLED_GEMS:yes=main)
+yes-update-default-gemspecs: $(PRECHECK_BUNDLED_GEMS:yes=main) $(PROGRAM)
 	@$(MAKEDIRS) $(srcdir)/.bundle/specifications
 	@$(XRUBY) -W0 -C "$(srcdir)" -rrubygems \
 	    -e "destdir = ARGV.shift" \