docs(ruby): explain the magic values in the testInterfaces assertions

Multiply implements IFriendly, IFriendlier and IRandomNumberGenerator at
once; each asserted value is a canary proving dispatch reached the right
interface's implementation. The 89 is Multiply's hardcoded fake
next() — not arithmetic on the operands.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Omar Qureshi

packages/@jsii/ruby-runtime-test/spec/compliance/interfaces_spec.rb

@@ -26,6 +26,12 @@
     add = JsiiCalc::Add.new(Scope::JsiiCalcLib::Number.new(10), Scope::JsiiCalcLib::Number.new(20))
     expect(add.hello).to eq("Hello, I am a binary operation. What's your name?")
 
+    # Multiply implements three interfaces at once — hello from IFriendly
+    # (via BinaryOperation), goodbye from IFriendlier, next from
+    # IRandomNumberGenerator — so each value below is a canary proving the
+    # member dispatched to the right interface's implementation.  The 89 is
+    # not arithmetic: it's Multiply's hardcoded, deliberately fake "random
+    # number generator" (calculator.ts: `public next() { return 89; }`).
     multiply = JsiiCalc::Multiply.new(Scope::JsiiCalcLib::Number.new(10), Scope::JsiiCalcLib::Number.new(30))
     expect(multiply.hello).to eq("Hello, I am a binary operation. What's your name?")
     expect(multiply.goodbye).to eq('Goodbye from Multiply!')