merge revision(s) e0dd0729,85f99f4b:

	Fix errors when XDG_CONFIG_HOME points to non-writable directory

	`$HOME/.config` is not writable on CI
	because I think tests should not corrupt user's data.

	And GitHub Actions CI sets `XDG_CONFIG_HOME`
	since `Version: 20210309.1`.

	https://github.com/ruby/actions/runs/2130811016?check_suite_focus=true#step:16:301
	```
	Errno::EACCES: Permission denied @ dir_s_mkdir - /home/runner/.config/irb
	```
	---
	 test/irb/test_cmd.rb | 2 ++
	 1 file changed, 2 insertions(+)

	Try to fix errors in TestIRB::TestHistory too

	https://github.com/ruby/actions/runs/2137935523?check_suite_focus=true#step:9:562
	```
	  1) Error:
	TestIRB::TestHistory#test_history_concurrent_use:
	Errno::EACCES: Permission denied @ dir_s_mkdir - /home/runner/.config/irb
	    /home/runner/work/actions/actions/ruby/lib/fileutils.rb:253:in `mkdir'
	    /home/runner/work/actions/actions/ruby/lib/fileutils.rb:253:in `fu_mkdir'
	    /home/runner/work/actions/actions/ruby/lib/fileutils.rb:231:in `block (2 levels) in mkdir_p'
	    /home/runner/work/actions/actions/ruby/lib/fileutils.rb:229:in `reverse_each'
	    /home/runner/work/actions/actions/ruby/lib/fileutils.rb:229:in `block in mkdir_p'
	    /home/runner/work/actions/actions/ruby/lib/fileutils.rb:211:in `each'
	    /home/runner/work/actions/actions/ruby/lib/fileutils.rb:211:in `mkdir_p'
	    /home/runner/work/actions/actions/ruby/lib/irb/init.rb:355:in `rc_file_generators'
	    /home/runner/work/actions/actions/ruby/lib/irb/init.rb:330:in `rc_file'
	    /home/runner/work/actions/actions/ruby/test/irb/test_history.rb:170:in `block in assert_history'
	    /home/runner/work/actions/actions/ruby/lib/tmpdir.rb:96:in `mktmpdir'
	    /home/runner/work/actions/actions/ruby/test/irb/test_history.rb:168:in `assert_history'
	    /home/runner/work/actions/actions/ruby/test/irb/test_history.rb:133:in `test_history_concurrent_use'
	```
	---
	 test/irb/test_history.rb | 2 ++
	 1 file changed, 2 insertions(+)