Update PemStream.InnerReadAsync() cancellation

.NET 7 and up have native cancellation support in StreamReader.ReadLineAsync(),
while .NET 6 has the Task.WaitAsync(CancellationToken) api we can alternatively
use (and we don't support cancellation for lower versions).

Author: mqudsi

SecureStore/PemStream.cs

@@ -65,7 +65,9 @@ private async Task<byte[]> InnerReadAsync(Stream stream, Func<StreamReader, Task
 
         public async Task<byte[]> ReadAsync(Stream stream, CancellationToken cancel = default)
         {
-#if NET6_0_OR_GREATER
+#if NET7_0_OR_GREATER
+            return await InnerReadAsync(stream, async (reader) => await reader.ReadLineAsync(cancel));
+#elif NET6_0_OR_GREATER
             return await InnerReadAsync(stream, async (reader) => await reader.ReadLineAsync().WaitAsync(cancel));
 #else
             return await InnerReadAsync(stream, async (reader) => await reader.ReadLineAsync());