ARROW-7711: [C#] Make Date32 test independent of system timezone
ARROW-7711: [C#] Make Date32 test independent of system timezone

The following failure was occurred on 2020-01-29:08:47:33+09:00:

    Starting test execution, please wait...
    [xUnit.net 00:00:00.53]     Apache.Arrow.Tests.Date32ArrayTests+Set.SetAndGet [FAIL]
      X Apache.Arrow.Tests.Date32ArrayTests+Set.SetAndGet [19ms]
      Error Message:
       Assert.Equal() Failure
    Expected: 2020-01-28T00:00:00.0000000
    Actual:   2020-01-27T00:00:00.0000000
      Stack Trace:
         at Apache.Arrow.Tests.Date32ArrayTests.Set.SetAndGet() in /tmp/arrow-0.16.0.mrKfP/apache-arrow-0.16.0/csharp/test/Apache.Arrow.Tests/Date32ArrayTests.cs:line 38

Closes #6309 from kou/csharp-date32-test-depends-on-timezone and squashes the following commits:

4967ab8e4 <Sutou Kouhei>  Make Date32 test independent of system timezone

Authored-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@clear-code.com>
Signed-off-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>

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