fix: exception.type should always be a string

[YanivD]

Which problem is this PR solving?

By Semantic Conventions for Exceptions - exception.type should be a string.

Short description of the changes

Cast to string for numeric exception codes.

[codecov]

Codecov Report

Merging #2086 (8fadccc) into main (fec5e31) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 8fadccc differs from pull request most recent head bf267ad. Consider uploading reports for the commit bf267ad to get more accurate results

@@            Coverage Diff             @@
##             main    #2086      +/-   ##
==========================================
- Coverage   93.05%   93.03%   -0.02%     
==========================================
  Files         154      154              
  Lines        5976     5976              
  Branches     1246     1246              
==========================================
- Hits         5561     5560       -1     
- Misses        415      416       +1     

Impacted Files	Coverage Δ
packages/opentelemetry-tracing/src/Span.ts	98.05% <100.00%> (ø)
...emetry-core/src/platform/node/RandomIdGenerator.ts	87.50% <0.00%> (-6.25%)	⬇️

[vmarchaud]

Could you add a quick test that verify that the result is always a string ?

[vmarchaud]

thanks for adding the test !