fix(tar): enable async overrides on net6 (#811)

Author: piksel

src/ICSharpCode.SharpZipLib/Tar/TarBuffer.cs

@@ -640,7 +640,7 @@ private async ValueTask CloseAsync(CancellationToken ct, bool isAsync)
 				{
 					if (isAsync)
 					{
-#if NETSTANDARD2_1_OR_GREATER
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
 						await outputStream.DisposeAsync().ConfigureAwait(false);
 #else
 						outputStream.Dispose();
@@ -660,7 +660,7 @@ private async ValueTask CloseAsync(CancellationToken ct, bool isAsync)
 				{
 					if (isAsync)
 					{
-#if NETSTANDARD2_1_OR_GREATER
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
 						await inputStream.DisposeAsync().ConfigureAwait(false);
 #else
 						inputStream.Dispose();

src/ICSharpCode.SharpZipLib/Tar/TarHeader.cs

@@ -869,7 +869,7 @@ public static string ParseName(ReadOnlySpan<byte> header, Encoding encoding)
 					}
 				}
 
-#if NETSTANDARD2_1_OR_GREATER
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
 				var value = encoding.GetString(header.Slice(0, count));
 #else
 				var value = encoding.GetString(header.ToArray(), 0, count);

src/ICSharpCode.SharpZipLib/Tar/TarInputStream.cs

@@ -232,7 +232,7 @@ public override Task<int> ReadAsync(byte[] buffer, int offset, int count, Cancel
 			return ReadAsync(buffer.AsMemory().Slice(offset, count), cancellationToken, true).AsTask();
 		}
 
-#if NETSTANDARD2_1_OR_GREATER
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
 		/// <summary>
 		/// Reads bytes from the current tar archive entry.
 		/// 
@@ -372,7 +372,7 @@ protected override void Dispose(bool disposing)
 			}
 		}
 
-#if NETSTANDARD2_1_OR_GREATER
+#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
 		/// <summary>
 		/// Closes this stream. Calls the TarBuffer's close() method.
 		/// The underlying stream is closed by the TarBuffer.