Update dependency halmos to v0.3.1 (#5818)

fv-requirements.txt

@@ -1,4 +1,4 @@
 certora-cli==4.13.1
 # File uses a custom name (fv-requirements.txt) so that it isn't picked by Netlify's build
 # whose latest Python version is 0.3.8, incompatible with most recent versions of Halmos
-halmos==0.3.0
+halmos==0.3.1