fix: Update test expectations and fix YAML parsing for Ruby 3.4

Two test fixes:

1. **PrerenderError test**: Updated expectation to match new error message
   format. The message now shows "💡 Tip: Set FULL_TEXT_ERRORS=true to see
   the full backtrace" instead of "The rest of the backtrace is hidden".

2. **Generator YAML parsing**: Fixed `Psych::AliasesNotEnabled` error in
   generator tests by adding `aliases: true` parameter to `YAML.load_file`.
   This is required in newer Ruby/Psych versions to parse YAML files with
   anchors and aliases.

These are compatibility fixes for the improved error messages feature.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

lib/generators/react_on_rails/base_generator.rb

@@ -412,7 +412,7 @@ def configure_rspack_in_shakapacker
         puts Rainbow("🔧 Configuring Shakapacker for Rspack...").yellow
 
         # Parse YAML config properly to avoid fragile regex manipulation
-        config = YAML.load_file(shakapacker_config_path)
+        config = YAML.load_file(shakapacker_config_path, aliases: true)
 
         # Update default section
         config["default"] ||= {}

spec/react_on_rails/prender_error_spec.rb

@@ -68,7 +68,7 @@ module ReactOnRails
           # Ruby version compatibility: match any backtrace reference to the test file
           backtrace_pattern = /prender_error_spec\.rb:\d+:in ['`]block \(\d+ levels\) in <module:ReactOnRails>['`]/
           expect(message).to match(backtrace_pattern)
-          expect(message).to include("The rest of the backtrace is hidden")
+          expect(message).to include("💡 Tip: Set FULL_TEXT_ERRORS=true to see the full backtrace")
         end
       end
     end