[runtime_env] Reference counter doesn't handle multiple options using the same URI

[edoakes]

What happened + What you expected to happen

When setting working_dir and py_modules to the same URI within the same runtime_env, only one of them will be GC'd. I added logs in the runtime_env agent, and it appears to call the deletion callback twice on ("py_modules", URI) instead of once on ("py_modules", URI) and once on ("working_dir", URI) as expected.

I haven't dug too deep yet, but it appears to be caused by the fact that this dictionary is keyed on URI only, not the (option, URI) tuple.

Versions / Dependencies

Master

Reproduction script

See the comment on test_runtime_env_working_dir_3::TestGC::test_actor_level_gc added here: #52553