The code in NewDecodeStore decoded the wrong proposal due
to a typographical error, but the tests used the exact same
value for the key value pairs hence the typo could never be caught.
I noticed it during an audit of the code, and I've fixed the
tests to pass in varying values for the various key value pairs.
Fixes#8570
Co-authored-by: Alessio Treglia <alessio@tendermint.com>