It caches a path to .irbrc file, which has caused random failure:
```
1) Failure:
TestIRB::ExtendCommand#test_irb_info_multiline [/home/mame/work/ruby/test/irb/test_cmd.rb:49]:
Expected /
Ruby\sversion: .+\n
IRB\sversion:\sirb .+\n
InputMethod:\sReidlineInputMethod\swith\sReline .+ and .+\n
\.irbrc\spath: .+
/x to match "Ruby version: 2.8.0\n" +
"IRB version: irb 1.2.3 (2020-02-15)\n" +
"InputMethod: ReidlineInputMethod with Reline 0.1.4 and /tmp/test_reline_config_155659/.inputrc\n".
```