Handle release tag formats in _parse_tag()

[dhgutteridge]

Also accommodate formal release tags, so the generated version is
correct for downstream packagers.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.60%. Comparing base (79974f2) to head (9636928).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
scapy/__init__.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4548      +/-   ##
==========================================
- Coverage   81.60%   81.60%   -0.01%     
==========================================
  Files         356      356              
  Lines       85533    85536       +3     
==========================================
- Hits        69802    69801       -1     
- Misses      15731    15735       +4     

Files with missing lines	Coverage Δ
scapy/__init__.py	83.11% <75.00%> (-0.67%)	⬇️

... and 4 files with indirect coverage changes

[gpotter2]

Looks good. Thanks for the PR !