Fixed the broken ruby-head NoMethodError spec.

[Jack12816]

- What is it good for

Fix the broken ruby-head continuous integration build (latest master).

- What I did

Looks like ruby 3.1.0-dev adds a more verbose exception message with the raising line as a suffix.

# Before 3.1.0-dev
pp e.message
"undefined method `not_exist_method'"

# After/With 3.1.0-dev
pp e.message
"undefined method `not_exist_method'\n" +
"\n" +
"          raise NoMethodError, \"undefined method `\#{handler}'\" unless respond_to?(handler)\n" +
"          ^^^^^"

So I just converted the raise_error message from a string to a regexp to ignore the new suffix.

- A picture of a cute animal (not mandatory but encouraged)

[grape-bot]

	1 Message
📖	We really appreciate pull requests that demonstrate issues, even without a fix. That said, the next step is to try and fix the failing tests!

Generated by 🚫 Danger

[dblock]

🚀

[Jack12816]

@dblock could you add the hacktoberfest-accepted label? 🙃