rbconfig is not used in these files

remove unused requires
Minitest::Unit::TestCase is Minitest::Test [ci skip]
Merge pull request #13502 from arunagw/bug-report-template-warning

Minitest::Unit::TestCase is Minitest::Test [ci skip]
Merge pull request #13500 from arunagw/remove-unused-require

rbconfig is not used in these files remove unused requires
Adding missing backslashes in active_model files so as to avoid unwanted links in rdoc [ci skip]
doc fix. Use `sess.path` within `open_session`. Closes #13490. [ci skip]
Merge pull request #13483 from aditya-kapoor/add-missing-slashes

Adding missing backslashes in active_model files so as to avoid unwanted [ci skip]
Ensure backward compatibility between Minitest 5 and 4

Define Minitest::Test in case we are running the gist under Minitest 4
and avoid relying on MiniTest::Unit::TestCase to avoid displaying
warning on version five.

[ci skip]
Merge pull request #13505 from robin850/patch-13

Ensure backward compatibility between Minitest 5 and 4
Copy changed_attributes across to newly become'd records

Without this, the original record's values won't get saved, since the partial insertions support (https://github.com/rails/rails/commit/144e8691cbfb8bba77f18cfe68d5e7fd48887f5e) checks for changed values and thinks there are none.
Merge pull request #13474 from jdelStrother/becomes

Copy changed_attributes across to newly become'd records
Merge branch 'master' into fxn/string-pools