conda jobs fail with requirement incompatibility errors (glibc?)

@duncanmmacleod @adam-mercer both the pipeline on !1680 (merged) (freshly branched off master) and the last one on master itself (https://git.ligo.org/lscsoft/lalsuite/-/pipelines/294959) fail in the lal:conda:[fftw/mkl] steps with a lot of error/warning output about package versioning. The part about conflicting glibc requirements (2.28 vs 2.17) looks like the likely main failure point to me, but I'm not entirely sure I'm parsing it correctly.

By contrast, the third pipeline listed from top (19h ago as of now), https://git.ligo.org/lscsoft/lalsuite/-/pipelines/294500 , and all earlier ones seem to have passed the lal stage and only failed later.