fix: remove deprecated --without option from ruby bundler

[reedham-aws]

Issue #, if available:
#805
^ PR to pin the old version that works.

The issue is that a new version of RubyGems (4.0.0) deprecates the --without option that we were using to not include test and development dependencies in sam build. This caused any sam build running with that version or above to fail.

Description of changes

Changed the bundler to not use --without. Previously, --without implicitly updated the bundler config to have a field like

BUNDLE_WITHOUT: "development:test"

Now, we set the config directly. This matches with the approach from the documentation.

Description of how you validated changes

After running pip install -e . in a Python environment, I tried building a Ruby function using samdev build (samdev being built with the new aws-lambda-builders. I confirmed that the build succeeded and successfully ignored testing dependencies. I also confirmed that this was not the case in the same environment with sam build.

I also confirmed that the behavior between old versions of RubyGems was the same as with the new version of aws-lambda-builders.

Finally, I updated the unit tests to reflect the new change.

Checklist

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