ci: pin python version in conda upgrade test job

[skip rhel][skip debian][skip platform][skip compiler][skip wheels]
18 jobs for fix-conda-upgrade-test in 147 minutes (queued for 6 seconds)
Status Job ID Name Coverage
  Tarballs
passed #1268695
tarball:lal

00:01:29

passed #1268694
tarballs

00:05:47

 
  Lal
passed #1268696
lal:conda:fftw

00:19:06

passed #1268697
lal:conda:mkl

00:20:22

 
  Lal Frame
passed #1268698
lalframe:conda

00:20:34

 
  Lal Meta Io
passed #1268699
lalmetaio:conda

00:20:48

 
  Lal Simulation
passed #1268700
lalsimulation:conda

00:22:42

 
  Lal Burst
passed #1268701
lalburst:conda

00:22:26

 
  Lal Inspiral
passed #1268702
lalinspiral:conda

00:25:59

 
  Lal Pulsar
passed #1268703
lalpulsar:conda

00:25:29

 
  Lal Inference
passed #1268704
lalinference:conda

00:29:02

 
  Lal Apps
passed #1268705
lalapps:conda

00:16:56

 
  Integration Tests
passed #1268706
top-level

00:38:07

 
  Upgrade Tests
passed #1268707
upgrade:conda:linux

00:09:12

 
  Coverage
passed #1268708
coverage

00:42:59

 
  Lint
passed #1268710
lint:coala

00:01:24

passed #1268709
lint:python

00:00:45

 
  Documentation
passed #1268711
documentation

00:05:32