Streamline CircleCI configuration

[mamhoff]

The previous configuration had a special way of updating bundler that was necessary 21 months ago, but probably is not anymore. This changes the configuration for a bog-standard configuration that should also run our specs.

The previous configuration also failed at cleaning up, with the following error:

https://github.com/solidusio/solidus (at v4.3@3ded512) is not yet checked out. Run `bundle install` first.

Exited with code exit status 11

https://app.circleci.com/pipelines/github/solidusio/solidus_dev_support/913/workflows/d9281ce7-fe62-45d8-b309-4f287b890924/jobs/2953

[mergify[bot]]

It looks like this PR is missing a label to determine the type of change it introduces. The maintainer should add one of the following labels:

• bug for bugfixes.
• enhancement for new features and improvements.
• documentation for documentation changes.
• security for security patches.
• removed for feature removals.
• infrastructure for internal changes that should not go in the changelog.

Additionally, the maintainer may also want to add one of the following:

• breaking for breaking changes.
• deprecated for feature deprecations.

Once the correct labels have been set, simply remove the needs changelog label label from this PR so I can merge it.

[mamhoff]

Closed in favor of https://github.com/solidusio/circleci-orbs-extensions/pull/93