Fix duplicated br tags

[SebKranz]

This PR demonstrates the issue described in #2716 and a possible fix.

I'm marking this as draft, because I would like check a few more details:

• are other tags affected (eg. w:tab)
• I should probably create a new test rather than modifying the existing one

Fixes: #2716

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (7f3c561) to head (ad201c8).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #2717   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files          281       281           
  Lines        14093     14093           
  Branches      1381      1381           
=========================================
  Hits         14093     14093           

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[dolanmiu]

Thank you, we came to the same conclusion

True, there could be other ones like w:tab which need testing

[dolanmiu]

You're right, tabs are also affected, I will fix this too

[SebKranz]

Based on the list of allowed children at http://officeopenxml.com/WPtext.php, I think we should change this to only include w:Pr.

w:Pr is the only tag related to styling and all others represent visual elements that shouldn't be duplicated.