Merge branch 'bugfix/richards-viscosity-check' into 'master'

[richards][fluidsystems] Fix static assert in Richards and implement...

See merge request !3146

(cherry picked from commit a0f0e297)

ab78f171 [richards][fluidsystems] Fix static assert in Richards and implement...
8309c462 fixup
f52906e8 fixrp
5 jobs for !3150 with cherry-pick-a0f0e297
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