bpo-30988: Add InvalidHeaderDefect for Trailing Periods

[malvidin]

When an email header address field contains a period directly before the angle bracket, the default header policy raises an Attribute error, rather than adding a header defect.

This issue is referenced in the eml_parser as 27257, but I am not sure if this is the correct issue.
GOVCERT-LU/eml_parser#41

https://github.com/GOVCERT-LU/eml_parser/blob/f98980a77d9c7d914d97525a62294075c0ce42d9/tests/test_emlparser.py#L136

This was only checked with Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 21:26:53).

https://bugs.python.org/issue27257

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[codecov]

Codecov Report

Merging #18687 into master will increase coverage by 1.08%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master   #18687       +/-   ##
===========================================
+ Coverage   82.12%   83.21%    +1.08%     
===========================================
  Files        1956     1571      -385     
  Lines      589830   415188   -174642     
  Branches    44477    44480        +3     
===========================================
- Hits       484427   345506   -138921     
+ Misses      95752    60035    -35717     
+ Partials     9651     9647        -4     

Impacted Files	Coverage Δ
Lib/distutils/tests/test_bdist_rpm.py	30.00% <0.00%> (-65.00%)	⬇️
Lib/distutils/command/bdist_rpm.py	7.63% <0.00%> (-56.88%)	⬇️
Lib/test/test_urllib2net.py	76.92% <0.00%> (-13.85%)	⬇️
Lib/test/test_smtpnet.py	78.57% <0.00%> (-7.15%)	⬇️
Lib/ftplib.py	63.85% <0.00%> (-6.06%)	⬇️
Lib/test/test_ftplib.py	87.11% <0.00%> (-4.72%)	⬇️
Tools/scripts/db2pickle.py	17.82% <0.00%> (-3.97%)	⬇️
Tools/scripts/pickle2db.py	16.98% <0.00%> (-3.78%)	⬇️
Lib/test/test_socket.py	71.94% <0.00%> (-3.77%)	⬇️
Lib/test/test_asyncio/test_base_events.py	91.84% <0.00%> (-3.30%)	⬇️
... and 439 more

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[malvidin]

Changed to bpo-30988, which appears to be more related than the bpo-27257 mentioned in the eml_parser.

[malvidin]

Looking through bug tracker, it appears that 30988 should be the bug referenced in the eml_parser.
https://bugs.python.org/issue30988

[malvidin]

Duplicate of #15600