New test checking that __CPROVER_havoc_object are detected as writes

[remi-delmas-3000]

New test checking that __CPROVER_havoc_object are detected as writes by assigns clause checking.

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

Merging #6499 (d8e5aac) into develop (7897cac) will decrease coverage by 0.19%.
The diff coverage is 66.21%.

@@             Coverage Diff             @@
##           develop    #6499      +/-   ##
===========================================
- Coverage    76.27%   76.07%   -0.20%     
===========================================
  Files         1546     1548       +2     
  Lines       165627   166362     +735     
===========================================
+ Hits        126329   126567     +238     
- Misses       39298    39795     +497     

Impacted Files	Coverage Δ
jbmc/src/janalyzer/janalyzer_parse_options.cpp	48.25% <ø> (ø)
jbmc/src/jdiff/jdiff_parse_options.h	100.00% <ø> (ø)
src/goto-diff/goto_diff_parse_options.h	100.00% <ø> (ø)
...rc/goto-instrument/goto_instrument_parse_options.h	100.00% <ø> (ø)
src/analyses/goto_check_java.cpp	33.82% <33.82%> (ø)
src/analyses/goto_check.cpp	66.66% <66.66%> (-23.50%)	⬇️
src/analyses/goto_check_c.cpp	90.29% <90.29%> (ø)
jbmc/src/jbmc/jbmc_parse_options.cpp	72.32% <100.00%> (ø)
jbmc/src/jdiff/jdiff_parse_options.cpp	68.11% <100.00%> (ø)
src/ansi-c/c_typecheck_code.cpp	78.80% <100.00%> (ø)
... and 2 more

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