Prevent passing version to bin/bundle

[vinistock]

Motivation

Closes #2731

If the user has their local bin directory as part of the PATH and a bin/bundle binstub exists, we accidentally invoke the binstub rather than invoking bundle exec.

This is problematic because the binstub doesn't accept the same arguments as the bundle executable. Namely, we can't pass the version using _2.5.12_ to ensure that the locked Bundler version is used and no restarts happen.

I'd argue that overriding the bundle executable with something that doesn't support the same arguments is not great as it prevents any tools from invoking Bundler directly, which is what they may legitimately want to do (this is the Ruby LSP's case).

However, it appears that this affects a considerable number of users, so let's put in a fix to prevent this error from happening.

Implementation

If there's a bin/bundle and any parts of the path are pointing to the local bin directory, then we favour using the binstub with no version.

Otherwise, we continue doing the same as before. I'm hesitant to expand this to always use the binstub if present since people could have modified their binstubs and that may lead to other errors.

Automated Tests

I added two new tests.