Include protobuf_deps.bzl in generated release archives

This fixes #5918.
diff --git a/Makefile.am b/Makefile.am
index 33616c5..290c7b5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1218,6 +1218,7 @@
   examples/pubspec.yaml                  \
   examples/third_party/zlib.BUILD        \
   protobuf.bzl                           \
+  protobuf_deps.bzl                      \
   python/release/wheel/build_wheel_manylinux.sh  \
   python/release/wheel/Dockerfile                \
   python/release/wheel/protobuf_optimized_pip.sh \