Auto merge of #6133 - bundler:seg-bundler-2-5-default-activation-fix, r=colby-swandale
Auto merge of #6133 - bundler:seg-bundler-2-5-default-activation-fix, r=colby-swandale

Ensure that autoloads are resolved in the real working directory

Fixes an issue on 2.5.0-dev where using local git overrides would cause an exception because the default bundler had been loaded

### What was the end-user problem that led to this PR?

The problem was Bundler was failing 8 specs against ruby trunk.

### What was your diagnosis of the problem?

My diagnosis was when the autoload for `URICredentialsFilter` fired in a `chdir` block, the default bundler gem was getting activated.

### What is your fix for the problem, implemented in this PR?

My fix eagerly trips that auto-load in the git proxy.

### Why did you choose this fix out of the possible options?

I chose this fix because it's a one-liner.

mvz/bundler,mvz/bundler,dilumnavanjana/bundler,bundler/bundler,dilumnavanjana/bundler,bundler/bundler