nit: fix doc comments spaces (#55272)

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Read.Stream.cs

@@ -28,7 +28,7 @@ public static partial class JsonSerializer
         /// The <see cref="System.Threading.CancellationToken"/> which may be used to cancel the read operation.
         /// </param>
         /// <exception cref="System.ArgumentNullException">
-        /// <paramref name="utf8Json"/>is <see langword="null"/>.
+        /// <paramref name="utf8Json"/> is <see langword="null"/>.
         /// </exception>
         /// <exception cref="JsonException">
         /// Thrown when the JSON is invalid,
@@ -61,7 +61,7 @@ public static partial class JsonSerializer
         /// <param name="utf8Json">JSON data to parse.</param>
         /// <param name="options">Options to control the behavior during reading.</param>
         /// <exception cref="System.ArgumentNullException">
-        /// <paramref name="utf8Json"/>is <see langword="null"/>.
+        /// <paramref name="utf8Json"/> is <see langword="null"/>.
         /// </exception>
         /// <exception cref="JsonException">
         /// Thrown when the JSON is invalid,