Update dependency rbs to v3.9.4 (#599)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [rbs](https://redirect.github.com/ruby/rbs)
([changelog](https://redirect.github.com/ruby/rbs/blob/master/CHANGELOG.md))
| `3.9.3` -> `3.9.4` |
[![age](https://developer.mend.io/api/mc/badges/age/rubygems/rbs/3.9.4?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/rubygems/rbs/3.9.4?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/rubygems/rbs/3.9.3/3.9.4?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/rubygems/rbs/3.9.3/3.9.4?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>ruby/rbs (rbs)</summary>

###
[`v3.9.4`](https://redirect.github.com/ruby/rbs/releases/tag/v3.9.4):
3.9.4

[Compare
Source](https://redirect.github.com/ruby/rbs/compare/v3.9.3...v3.9.4)

[Release
note](https://redirect.github.com/ruby/rbs/wiki/Release-Note-3.9)

##### Miscellaneous

- Backport test/CI fixes to 3.9
([#&#8203;2487](https://redirect.github.com/ruby/rbs/pull/2487))
- Use erb instead of set for load path testing
([#&#8203;2468](https://redirect.github.com/ruby/rbs/pull/2468))

</details>

---

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---

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---

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Gemfile.lock

@@ -66,7 +66,7 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rbs (3.9.3)
+    rbs (3.9.4)
       logger
     regexp_parser (2.10.0)
     rexml (3.4.1)