add core_deps back as pre_submit

Author: daniel-sanche

.kokoro/presubmit/head.cfg

@@ -0,0 +1,7 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Only run this nox session.
+env_vars: {
+    key: "NOX_SESSION"
+    value: "core_deps_from_source"
+}