build: Specify test dependencies in Gemfile to bundle them

Because those gems might not be installed in Ruby installation
(rbinstall.rb is broken when a bundled gem is built from commit hash),
we need to specify them in Gemfile to bundle them explicitly.

Author: kateinoigakukun

packages/npm-packages/ruby-wasm-wasi/Gemfile

@@ -4,3 +4,5 @@ source "https://rubygems.org"
 
 gem "js", path: "../../gems/js"
 gem "ruby_wasm", path: "../../../"
+gem "power_assert"
+gem "test-unit"

packages/npm-packages/ruby-wasm-wasi/Gemfile.lock

@@ -11,14 +11,19 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
+    power_assert (2.0.3)
+    test-unit (3.6.2)
+      power_assert
 
 PLATFORMS
   ruby
   x86_64-linux
 
 DEPENDENCIES
   js!
+  power_assert
   ruby_wasm!
+  test-unit
 
 BUNDLED WITH
    2.5.3