Merge #3043

3043: Use Bundler 2.1.2 r=hsbt a=hsbt

# Description:

for RubyGems 3.1.2
______________

# Tasks:

- [ ] Describe the problem / feature
- [ ] Write tests
- [ ] Write code to solve the problem
- [ ] Get code review from coworkers / friends

I will abide by the [code of conduct](https://github.com/rubygems/rubygems/blob/master/CODE_OF_CONDUCT.md).


Co-authored-by: Hiroshi SHIBATA <[email protected]>

Author: bundlerbot