chore: bundle install with --with option is dispensable in this case

[sato11]

TLDR; bundle install and bundle install --with development both install the same set. So perhaps one without flag is clearer to use?

The setup script and the ci workflow definition specify that bundler should use --with development option, which has been deprecated as of newer version of bundler. Mine is 2.4.3.

[DEPRECATED] The `--with` flag is deprecated because it relies on being remembered across bundler invocations, which bundler will no longer do in future versions. Instead please use `bundle config set --local with 'development'`, and stop using this flag

While the intention is apparently to restrict installed gems to development group, it makes no difference to the resulting installation set.

This is because we cannot rely on --with to opt out from installing grouped gems. What we might want to use is either --without option or group :test, optional: true. A relevant reference is here:
https://bundler.io/guides/groups.html#optional-groups-and-bundlewith

Here I propose that we drop the irrelevant flag. The discussion above in turn shows that gem 'simplecov' does not need to reside in test group, as it's been, and will be, installed regardless of the presence of --with. Therefore it's got rid of as well.

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[shrutiburman]

Thanks for the PR! We've added the review to our backlog to be prioritised. Pull requests and +1s on the issue summary will help it move up the backlog.