Fix wrong name __CPROVER_invariant of invariant clauses

[qinheping]

This commit replaces the wrong name __CPROVER_invariant of invariant clauses with the correct name __CPROVER_loop_invariant.

• Each commit message has a non-empty body, explaining why the change was made.
  n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
  n/a 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).
  n/a 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 #7107 (b9cf431) into develop (c2f99d4) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #7107      +/-   ##
===========================================
+ Coverage    77.87%   77.91%   +0.04%     
===========================================
  Files         1576     1576              
  Lines       181588   181588              
===========================================
+ Hits        141413   141490      +77     
+ Misses       40175    40098      -77     

Impacted Files	Coverage Δ
src/crangler/c_wrangler.cpp	75.10% <100.00%> (+15.35%)	⬆️
src/crangler/c_defines.cpp	80.00% <0.00%> (+36.00%)	⬆️
src/crangler/ctokenit.cpp	72.41% <0.00%> (+72.41%)	⬆️
src/crangler/ctokenit.h	83.33% <0.00%> (+83.33%)	⬆️

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