Add requires-network to pip requirements update. (#1050)

:requirements_test would previously fail if sandboxing was enabled.

python/pip_install/requirements.bzl

diff --git a/python/pip_install/requirements.bzl b/python/pip_install/requirements.bzl
index 35399da..51e34a2 100644
--- a/python/pip_install/requirements.bzl
+++ b/python/pip_install/requirements.bzl
@@ -101,6 +101,8 @@
         requirement("more_itertools"),
     ] + extra_deps
 
+    tags = tags or []
+    tags.append("requires-network")
     attrs = {
         "args": args,
         "data": data,