Skip updating exts in also test-spec to reduce the turnaround time (#4089)

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

Partially reversing a4f3e1762a like 21df4dce53.
We usually run them through make check which has the dependency, and test-all and test-spec without the dependency are useful for running only individual tests.

common.mk

@@ -835,7 +835,7 @@ $(RBCONFIG): $(tooldir)/mkconfig.rb config.status $(srcdir)/version.h
 test-rubyspec: test-spec
 yes-test-rubyspec: yes-test-spec
 
-test-spec-precheck: main
+test-spec-precheck: programs
 
 test-spec: $(TEST_RUNNABLE)-test-spec
 yes-test-spec: test-spec-precheck