chore(gnovm): prevent assignment to non-assignable expressions

[omarsy]

closes: #2889

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.96%. Comparing base (8a62a28) to head (2835a06).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2896   +/-   ##
=======================================
  Coverage   60.95%   60.96%           
=======================================
  Files         564      564           
  Lines       75273    75282    +9     
=======================================
+ Hits        45884    45895   +11     
  Misses      26019    26019           
+ Partials     3370     3368    -2     

Flag	Coverage Δ
contribs/gnodev	61.46% <ø> (ø)
contribs/gnofaucet	14.46% <ø> (ø)
gno.land	67.92% <ø> (ø)
gnovm	65.79% <100.00%> (+0.01%)	⬆️
misc/genstd	80.54% <ø> (ø)
misc/logos	19.88% <ø> (ø)
tm2	61.98% <ø> (-0.09%)	⬇️

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