fix(datetime): correct parsing of day period

[timreichen]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 4 lines in your changes missing coverage. Please review.

Project coverage is 96.43%. Comparing base (e3dc30a) to head (8c4eb2e).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
datetime/_date_time_formatter.ts	88.23%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6313      +/-   ##
==========================================
+ Coverage   96.35%   96.43%   +0.08%     
==========================================
  Files         547      547              
  Lines       41671    41788     +117     
  Branches     6315     6338      +23     
==========================================
+ Hits        40151    40298     +147     
+ Misses       1479     1449      -30     
  Partials       41       41              

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[kt3k]

Note: This fixes the parsing of day periods veriants like AM. PM. A.M. P.M. (which was added in #5406, but wasn't working). Currently parse("A.M.", "a") throws. This branch fixes it.

[kt3k]

LGTM