Fix: add case-insensitive enum parsing to Chart Axis TickMark getters

[lievendf]

Summary of Changes

This PR resolves a case-sensitivity enum parsing bug inside ExcelChartAxisStandard where setting MajorTickMark or MinorTickMark wrote lowercased strings to XML (e.g. "in", "out"), but reading them back failed because Enum.Parse was called case-sensitively against the capitalized enum members (In, Out).

Passing true as the third parameter of Enum.Parse enables case-insensitive parsing, bringing MajorTickMark and MinorTickMark into alignment with other chart axis properties.

Related Issues

Closes #2369

Details of Changes

• src/EPPlus/Drawing/Chart/ExcelChartAxisStandard.cs:

  • Updated MajorTickMark getter to use Enum.Parse(typeof(eAxisTickMark), v, true).
  • Updated MinorTickMark getter to use Enum.Parse(typeof(eAxisTickMark), v, true).

• src/EPPlusTest/Issues/ChartIssues.cs:

  • Added MSUnit test case ChartAxisTickMarkCaseSensitivity to verify that both MajorTickMark and MinorTickMark can be assigned and read back correctly for all valid enum states (In, Out, None).

Verification & Testing

• Ran dotnet test src/EPPlusTest/EPPlus.Test.csproj --filter Name=ChartAxisTickMarkCaseSensitivity
• Verified successful execution under .NET 8.0 and .NET Framework 4.8.1 (total: 2; failed: 0; succeeded: 2).

[JanKallman]

Thanks!