Pin blackjax<1.6 in alternative-backends conda env

blackjax 1.6 tightened kwarg validation on its NUTS/HMC kernel, which
surfaces a latent bug in pymc.sampling.jax._blackjax_inference_loop:
progress_bar is forwarded into blackjax.window_adaptation()'s
**adaptation_kwargs before being popped back out a few lines later,
so it leaks into the kernel builder. blackjax 1.5 tolerated the stray
kwarg; 1.6 raises TypeError. Pin until the wrapper pops progress_bar
before calling window_adaptation.

Author: jacobpstein

conda-envs/environment-alternative-backends.yml

@@ -39,7 +39,11 @@ dependencies:
 - types-cachetools
 # blackjax now does not pull in fastprogress by default
 - fastprogress>=1.0.0
-- blackjax>=1.5
+# blackjax 1.6 tightened kwarg checking on the NUTS/HMC kernel builder, which
+# exposes a latent bug in pymc.sampling.jax._blackjax_inference_loop: it
+# forwards progress_bar into blackjax.window_adaptation()'s **adaptation_kwargs
+# before popping it back out. Pin until that call is fixed to pop it first.
+- blackjax>=1.5,<1.6
 - pip:
   - numdifftools>=0.9.40
   - mcbackend>=0.4.0