Run spec on ruby-head for the effect of frozen string literal

See also https://bugs.ruby-lang.org/issues/20205
Itamae has no frozen_string_literal magic comments.
In the future, Ruby will enable frozen string literal by default.
This commit checks its effect for itamae, by recurring GitHub actions.

.github/workflows/test.yml

@@ -59,6 +59,12 @@ jobs:
             rubyopt: "--yjit"
           - ruby:    "3.3"
             rubyopt: "--yjit"
+        include:
+          # ruby-debug is the same as ruby-head but with assertions enabled (-DRUBY_DEBUG=1)
+          - ruby: "debug"
+            rubyopt: "" # See also https://bugs.ruby-lang.org/issues/20205 (enable frozen string literal as default)
+          - ruby: "debug"
+            rubyopt: "--disable=frozen-string-literal"
 
     uses: ./.github/workflows/test_main.yml
     with:

itamae.gemspec

@@ -32,6 +32,7 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency "hashie"
   spec.add_runtime_dependency "ansi"
   spec.add_runtime_dependency "schash", "~> 0.1.0"
+  spec.add_runtime_dependency "base64"
 
   spec.add_development_dependency "bundler", ">= 1.3"
   spec.add_development_dependency "rake"