Make checkbuild depend on blueprint_tests

The Soong tests are being disabled by default, add them as a manual
dependency of checkbuild to esnure they still run in CI.

Bug: 269296618
Test: aninja -t path checkbuild out/host/linux-x86/bin/go/soong-java/test/test.passed
Change-Id: Ice9b5ecdef8455cd0b173edbac141861cffc28c1
diff --git a/core/main.mk b/core/main.mk
index 7c25862..c345c96 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -563,6 +563,7 @@
 # sources or dependencies for these tools may be missing from the tree.
 ifeq (,$(TARGET_BUILD_UNBUNDLED_IMAGE))
 droid_targets : blueprint_tools
+checkbuild: blueprint_tests
 endif
 
 endif # dont_bother