Fix some runtime warnings

[ydah]

What? Why?

A runtime warning was output when executing in the following environment, which has been corrected:

❯ ruby -v
ruby 3.4.0rc1 (2024-12-12 master 29caae9991) +PRISM [arm64-darwin23]
❯ RUBYOPT=-w bundle exec rake
/ydah/gruf/spec/support/helpers.rb:97: warning: possibly useless use of nil in void context
/ydah/gruf/spec/support/helpers.rb:88: warning: assigned but unused variable - e

How was it tested?

Verified that existing tests were not broken.