Fix TrimDirectorySeparators to handle root-path on Windows and Linux

[snakefoot]

Fix loading Nlog.config when application is running at root-path (Ex. D:\). Resolves #4314

Bug introduced with #2846 in NLog 4.5.9

[304NotModified]

@snakefoot the stability of azure devops should be improved now. I've setup a restart of failed tests, and that worked, but not really as it failed on the minimum amount of tests...(meh)

LOL nice bug in Azure devops:

Total tests: 3045. Passed: 3035. Failed: 1. Skipped: 9.
##[error]Test Run Failed.
....
Failed tests: 1; Total tests: 3023;
Total failed tests as returned by TCM: 1.
Found 1 filtered test case sources.
**************** Rerunning failed tests for Test run 3674 *********************
Max attempts: 5; Current attempt: 1; Failed test cases threshold: 30; Failed test cases max limit: 0
....
Starting test execution, please wait...
....
Total tests: 1. Passed: 1. Failed: 0. Skipped: 0.
Test Run Successful.
Test execution time: 34.0482 Seconds
Vstest.console.exe exited with code 0.
**************** Completed test execution *********************
...
##[error]The specified minimum number of tests 100 were not executed in the test run.

full result

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

83.3% Coverage
0.0% Duplication