fix : Various casing on "Version" should not throw

[MartyMcFlaye]

When trying to run dotnet affected on a large solution, I ran into an exception:

Unhandled exception: System.InvalidOperationException: Sequence contains no matching element
   at System.Linq.ThrowHelper.ThrowNoMatchException()
   at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source, Func`2 predicate)
   at DotnetAffected.Core.NugetHelper.PackageRef.Create(ProjectItem item, String versionOverride) in /_/src/DotnetAffected.Core/NugetHelper.cs:line 46
   at DotnetAffected.Core.NugetHelper.ParseDirectoryPackageProps(Project project) in /_/src/DotnetAffected.Core/NugetHelper.cs:line 85
   at DotnetAffected.Core.Processor.AffectedProcessor.FindChangedNugetPackages(AffectedProcessorContext context) in /_/src/DotnetAffected.Core/Processor/AffectedProcessor.cs:line 120
   at DotnetAffected.Core.Processor.AffectedProcessor.DiscoverPackageChanges(AffectedProcessorContext context) in /_/src/DotnetAffected.Core/Processor/AffectedProcessor.cs:line 30
   at DotnetAffected.Core.Processor.AffectedProcessorBase.Process(AffectedProcessorContext context) in /_/src/DotnetAffected.Core/Processor/AffectedProcessorBase.cs:line 33
   at DotnetAffected.Core.AffectedExecutor.Execute() in /_/src/DotnetAffected.Core/AffectedExecutor.cs:line 41
   at Affected.Cli.Commands.InvocationContextExtensions.ExecuteAffectedExecutor(InvocationContext ctx) in /_/src/dotnet-affected/Commands/Binding/InvocationContextExtensions.cs:line 38
   at Affected.Cli.Commands.AffectedRootCommand.<>c.<<-ctor>b__4_0>d.MoveNext() in /_/src/dotnet-affected/Commands/AffectedRootCommand.cs:line 38

When debugging, it appeared that this was caused by a "Version" attribute in my Directory.Packages.props with this casing : "version".

Since Visual Studio does not seem to be case sensitive, i propose to merge this pull request to fix this issue.

[leonardochaia]

Hi @MartyMcFlaye , thanks for the fix and test 🥇