Fixup ruby-lsp setup

Author: soutaro

steep/Gemfile

@@ -2,3 +2,5 @@ source "https://rubygems.org"
 
 gem "rbs", "~> 3.9.pre"
 gem "steep", "~> 1.10"
+gem "ruby-lsp"
+gem "test-unit"

steep/Gemfile.lock

@@ -37,14 +37,22 @@ GEM
     parser (3.3.7.4)
       ast (~> 2.4.1)
       racc
+    power_assert (2.0.5)
+    prism (1.4.0)
     racc (1.8.1)
     rainbow (3.1.1)
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
     rbs (3.9.0)
       logger
+    ruby-lsp (0.23.13)
+      language_server-protocol (~> 3.17.0)
+      prism (>= 1.2, < 2.0)
+      rbs (>= 3, < 4)
+      sorbet-runtime (>= 0.5.10782)
     securerandom (0.4.1)
+    sorbet-runtime (0.5.11980)
     steep (1.10.0)
       activesupport (>= 5.1)
       concurrent-ruby (>= 1.1.10)
@@ -65,6 +73,8 @@ GEM
     strscan (3.1.2)
     terminal-table (4.0.0)
       unicode-display_width (>= 1.1.1, < 4)
+    test-unit (3.6.7)
+      power_assert
     tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
     unicode-display_width (3.1.4)
@@ -77,7 +87,9 @@ PLATFORMS
 
 DEPENDENCIES
   rbs (~> 3.9.pre)
+  ruby-lsp
   steep (~> 1.10)
+  test-unit
 
 BUNDLED WITH
    2.6.3