[release 0.5] hack in a fix to getting the right lambda for the incremental deserializer

[vtjnash]

fix #18449
(the real, non-buggy fix is in #18413 for v0.6-dev master)

[yuyichao]

Note that #18449 does not trigger on 0.5.

[vtjnash]

oh, I guess this also needs #18415 backported first too

[tkelman]

can you add a test? I saw this error on gadfly and mamba in #18546, will upload logs soon

[tkelman]

Old travis logs backed up to

• https://gist.github.com/e7f9adec6b3f077acc11a6ffc55de68e
• https://gist.github.com/9a56907516fdf7d6366c79241ad3e1c8
• https://gist.github.com/158c194d81a2039fe71dec17cf8e832c

and restarted. May need to merge this into tk/backports-0.5.0 before @vtjnash (or @yuyichao?) wakes up and can identify if there's already an appropriate test for this on master or if a new one needs to be written. We'll still need a test for release-0.5 but I won't block starting my next pkgeval run on it.

[tkelman]

Master needs the test too, so we'll do that in a new PR and backport whenever it's ready.