Remove test dependency on locale

[luigiberrettini]

Since some tests were not working because relying on a specific locale I fixed them.

NLog version
4.3.0

Work arounds
None

Config when implemented
No changes

[codecov-io]

Current coverage is 75.17%

Merging #1393 into master will not affect coverage as of 4ca0279

@@            master   #1393   diff @@
======================================
  Files          267     267       
  Stmts        15607   15607       
  Branches      1642    1642       
  Methods          0       0       
======================================
  Hit          11732   11732       
  Partial        383     383       
  Missed        3492    3492       

Review entire Coverage Diff as of 4ca0279

---

Uncovered Suggestions

1. +0.09% via ...gingConfiguration.cs#374...387
2. +0.09% via ...gingConfiguration.cs#340...353
3. +0.08% via ...argets/FileTarget.cs#1741...1753
4. See 7 more...

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