Add back source-only ruby packages for 1.30.x
diff --git a/Rakefile b/Rakefile
index 3b23d0b..a488eb0 100755
--- a/Rakefile
+++ b/Rakefile
@@ -142,7 +142,7 @@
 
         gem update --system --no-document && \
         bundle && \
-        rake native:#{plat} pkg/#{spec.full_name}-#{plat}.gem \
+        rake native:#{plat} pkg/#{spec.full_name}-#{plat}.gem pkg/#{spec.full_name}.gem \
           RUBY_CC_VERSION=2.7.0:2.6.0:2.5.0:2.4.0:2.3.0 \
           V=#{verbose} \
           GRPC_CONFIG=#{grpc_config}