Ignore PyTest 5.4.2

[nulano]

Python 3.9-pre tests have started failing recently, with a segmentation fault in PyTest rewrite during collection: https://travis-ci.org/github/python-pillow/Pillow/jobs/686090749#L2777

Pinning pytest!=5.4.2 to force PyTest 5.4.1 seems to fix this.

[nulano]

Git clone failed here: https://travis-ci.org/github/python-pillow/Pillow/jobs/686531139#L168

It passes on my repo: https://travis-ci.org/github/nulano/Pillow/jobs/686527965

[nulano]

Looks like it is not passing in this repo, even though it passed in mine.

Additionally, PyTest 5.4.2 actually passes in my repo as well (my pr #4615): https://travis-ci.org/github/nulano/Pillow/jobs/684984552#L2666 (I didn't check because I thought it was older, sorry for the noise)

[hugovk]

Good finding!

It's failing on my fork too.

I diffed your passing log and the failing upstream one, and the first think I noticed is that upstream is using a cache for pip, and yours is downloading fresh files.

I deleted the Travis caches on my fork, and 3.9 now passes!

• https://travis-ci.org/github/hugovk/Pillow/jobs/686538362

I've deleted caches for upstream too and triggered a fresh build:

• https://travis-ci.org/github/python-pillow/Pillow/builds/686544743

[hugovk]

And it passed!

https://travis-ci.org/github/python-pillow/Pillow/jobs/686544749