Partial revert of b2bc25c

Author: ynse01

src/ImageSharp/Formats/Pbm/PbmDecoder.cs

@@ -54,8 +54,9 @@ public Task<Image<TPixel>> DecodeAsync<TPixel>(Configuration configuration, Stre
         }
 
         /// <inheritdoc />
-        public Task<Image> DecodeAsync(Configuration configuration, Stream stream, CancellationToken cancellationToken)
-            => this.DecodeAsync(configuration, stream, cancellationToken);
+        public async Task<Image> DecodeAsync(Configuration configuration, Stream stream, CancellationToken cancellationToken)
+            => await this.DecodeAsync<Rgba32>(configuration, stream, cancellationToken)
+            .ConfigureAwait(false);
 
         /// <inheritdoc/>
         public IImageInfo Identify(Configuration configuration, Stream stream)