Pre-Release Testing for v7.3

[John Clements]

Note the altered testing ending date (May 9th) below. And: thanks for your patience. And please let me know if you run into any problems with the testing process!

Testing for the v7.3 release
(using the v7.2.0.900 release candidate build)

Search for your name on the checklist page to find relevant items, either
reply when you finish an item (please indicate which item/s is/are done),
or check it off yourself on the checklist page. Also, if you have any
commits that should have been picked, make sure that the changes are in.

Be sure to finish your testing by the 9th. Otherwise the release
will move on without your input.

The checklist page is at:
https://github.com/racket/racket/wiki/Release-Checklist-7.3

Release candidates are at:
https://pre-release.racket-lang.org

Please use these installers (or source bundles) -- don't test from
your own git clone (don't test the `master' branch by mistake!).
To get the tests, you can do this:

cd ...racket-root...
./bin/raco pkg install -i --auto main-distribution-test