fix: test_function_release_strong_count

[Wodann]

As no strong reference was active anymore, the OS could free the memory, overwriting the original strong count value. Now, we're ensuring that at least one strong reference exists at the end of the test, to avoid memory from being freed

[codecov]

Codecov Report

Merging #535 (f93d7b1) into main (42fadbd) will increase coverage by 2.94%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #535      +/-   ##
==========================================
+ Coverage   84.37%   87.31%   +2.94%     
==========================================
  Files         275      275              
  Lines       31185    31182       -3     
==========================================
+ Hits        26312    27227     +915     
+ Misses       4873     3955     -918     

Impacted Files	Coverage Δ
crates/mun_runtime_capi/src/function.rs	99.59% <100.00%> (-0.01%)	⬇️

... and 13 files with indirect coverage changes