SARIF report marks issues as updated it multiple issues with same persistent properties

[christianbumann]

Create a Sarif report with two identical issues which only differs on FileLink marks one as Unchanged and the other as Updated. Both issues should be marked as Unchanged.

How to reproduce

Create a test e.g. in SarifIssueReportGeneratorTests

[Fact]
public void Should_Generate_Report_With_BaseLineState_Unchanged_If_Only_File_Link_Has_Changed_On_Multi_Issues()
{
    // Given
    var fixture = new SarifIssueReportFixture();
    fixture.SarifIssueReportFormatSettings.BaselineGuid = Guid.NewGuid();

    var issues =
        new List<IIssue>
        {
            IssueBuilder
                .NewIssue("Message Foo.", "ProviderType Foo", "ProviderName Foo")
                .InFile(@"a", 10, 12, 1, 2)
                .WithFileLink(new Uri("https://github.com/cake-contrib/Cake.Issues/blob/develop/src/Cake.Issues.MsBuild/BaseMsBuildLogFileFormat.cs"))
                .Create(),

            IssueBuilder
                .NewIssue("Message Foo.", "ProviderType Foo", "ProviderName Foo")
                .InFile(@"a", 20, 22, 1, 2)
                .WithFileLink(new Uri("https://github.com/cake-contrib/Cake.Issues/blob/develop/src/Cake.Issues.MsBuild/BaseMsBuildLogFileFormat.cs"))
                .Create(),

        };

    var existingIssues =
        new List<IIssue>
        {
            IssueBuilder
                .NewIssue("Message Foo.", "ProviderType Foo", "ProviderName Foo")
                .InFile(@"a", 10, 12, 1, 2)
                .WithFileLink(new Uri("https://github.com/cake-contrib/Cake.Issues/blob/master/src/Cake.Issues.MsBuild/BaseMsBuildLogFileFormat.cs"))
                .Create(),

            IssueBuilder
                .NewIssue("Message Foo.", "ProviderType Foo", "ProviderName Foo")
                .InFile(@"a", 20, 22, 1, 2)
                .WithFileLink(new Uri("https://github.com/cake-contrib/Cake.Issues/blob/master/src/Cake.Issues.MsBuild/BaseMsBuildLogFileFormat.cs"))
                .Create(),
        };

    fixture.SarifIssueReportFormatSettings.ExistingIssues.AddRange(existingIssues);

    // When
    var logContents = fixture.CreateReport(issues);

    // Then
    var sarifLog = JsonConvert.DeserializeObject<SarifLog>(logContents);

    var run = sarifLog.Runs.ShouldHaveSingleItem();
    run.Results.Count.ShouldBe(2);
    run.Results[0].BaselineState.ShouldBe(BaselineState.Unchanged);
    run.Results[1].BaselineState.ShouldBe(BaselineState.Unchanged);
}

[christianbumann]

existingIssuesSet should contains 2 items, but there is only 1 item.

https://github.com/cake-contrib/Cake.Issues/blob/15de6704ad99d85ae441643cf372a25235064f9d/src/Cake.Issues.Reporting.Sarif/SarifIssueReportGenerator.cs#L66