Only upload junit XML files

[dandavison]

There are many large coverage files in the zip archives which we don't want to have to download when we are only interested in accessing junit XMLs:

$ gh run download 11404810538 --repo temporalio/temporal --dir .
$ fd --type f --exec du -ah {} | sort -rh

3.7M    ./junit-xml--11404810538--1--postgres12_pgx--functional-test-xdc/90b64926828a35a7fa7d0abe4e47fb81.cover.out
...30 like this...
3.6M    ./junit-xml--11404810538--1--cass_es--functional-test-ndc/1489124e0ff5f88db39decd3857743e3.cover.out
3.3M    ./junit-xml--11404810538--1--unit-test/e79e1deb24d801f1386c6d15fa8aa9b8.cover.out
2.9M    ./junit-xml--11404810538--1--integration-test/ec6be7e1fa51451d8af37c9645ed1ec2.cover.out
884K    ./junit-xml--11404810538--1--unit-test/9721157f8b693ef10498237f1c2a6815.junit.xml
412K    ./junit-xml--11404810538--1--integration-test/832a9ed3484a3b633106f01aac17822a.junit.xml
272K    ./junit-xml--11404810538--1--ubuntu-20.04--cass_es8--2--functional-test/80d320ae0fb05f84e633c54af2f222f7.junit.xml
260K    ./junit-xml--11404810538--1--postgres12_pgx--functional-test-xdc/49b18d5cb0cf6427a3c5cd645ac3ab8c.junit.xml

However, there are also a few very large junit XMLs, in which complete logging output has been captured in the <failure message="Failed" type=""> field.

8.4M    ./junit-xml--11404810538--1--ubuntu-20.04--sqlite--2--functional-test/053f83e6a8000b581a749edd016398ba.junit.xml

It would be good to prevent creation of these large XMLs in a subsequent PR.