Address code review: remove redundant null-forgiving op and fix doc grammar

Co-authored-by: ViktorHofer <7412651+ViktorHofer@users.noreply.github.com>

Author: Copilot

documentation/specs/question.md

@@ -79,7 +79,7 @@ Error when SkipUnchangedFiles is true.
 Error if the destination zip file doesn't exists.
 
 `TarDirectory`
-Error if the destination tar file doesn't exists.
+Error if the destination tar file doesn't exist.
 
 ## Common Error
 

src/Tasks/TarDirectory.cs

@@ -108,7 +108,7 @@ public override bool Execute()
                         Log.LogMessageFromResources(MessageImportance.High, "TarDirectory.Comment", sourceDirectory.FullName, destinationFile.FullName);
 
                         bool useGZip = false;
-                        if (!string.IsNullOrEmpty(Compression) && !TryParseCompression(Compression!, out useGZip))
+                        if (!string.IsNullOrEmpty(Compression) && !TryParseCompression(Compression, out useGZip))
                         {
                             Log.LogWarningWithCodeFromResources("TarDirectory.WarningInvalidCompression", Compression);
                         }