Use explicit stream type

Author: JimBobSquarePants

src/ImageSharp.Web/Resolvers/PhysicalFileSystemCacheResolver.cs

@@ -35,7 +35,7 @@ public async Task<ImageCacheMetadata> GetMetaDataAsync()
         {
             if (this.metadata == default)
             {
-                using Stream stream = OpenFileStream(this.metaFileInfo.FullName);
+                using FileStream stream = OpenFileStream(this.metaFileInfo.FullName);
                 this.metadata = await ImageCacheMetadata.ReadAsync(stream);
             }