Update StreamReader.xml

Fixes dotnet#9798; Wrong documentation on `Read(Span<char>)` for `IOException`.

Author: colejohnson66

Diff for: xml/System.IO/StreamReader.xml

@@ -1890,7 +1890,7 @@ Following a call to <xref:System.IO.StreamReader.Close%2A>, any operations on th
         <summary>Reads the characters from the current stream into a span.</summary>
         <returns>The number of characters that have been read, or 0 if at the end of the stream and no data was read. The number will be less than or equal to the <paramref name="buffer" /> length, depending on whether the data is available within the stream.</returns>
         <remarks>To be added.</remarks>
-        <exception cref="T:System.IO.IOException">The number of characters read from the stream is larger than the <paramref name="buffer" /> length.</exception>
+        <exception cref="T:System.IO.IOException">An I/O error occurs.</exception>
         <exception cref="T:System.ArgumentNullException">
           <paramref name="buffer" /> is <see langword="null" />.</exception>
       </Docs>
@@ -1986,7 +1986,7 @@ Following a call to <xref:System.IO.StreamReader.Close%2A>, any operations on th
           <paramref name="buffer" /> is <see langword="null" />.</exception>
         <exception cref="T:System.ArgumentOutOfRangeException">
           <paramref name="index" /> or <paramref name="count" /> is negative.</exception>
-        <exception cref="T:System.IO.IOException">An I/O error occurs, such as the stream is closed.</exception>
+        <exception cref="T:System.IO.IOException">An I/O error occurs.</exception>
         <related type="Article" href="/dotnet/standard/io/">File and Stream I/O</related>
         <related type="Article" href="/dotnet/standard/io/how-to-read-text-from-a-file">How to: Read Text from a File</related>
         <related type="Article" href="/dotnet/standard/io/how-to-write-text-to-a-file">How to: Write Text to a File</related>
@@ -2178,7 +2178,7 @@ Following a call to <xref:System.IO.StreamReader.Close%2A>, any operations on th
         <exception cref="T:System.ArgumentNullException">
           <paramref name="buffer" /> is <see langword="null" />.</exception>
         <exception cref="T:System.ObjectDisposedException">The <see cref="T:System.IO.StreamReader" /> is closed.</exception>
-        <exception cref="T:System.IO.IOException">An I/O error occurred.</exception>
+        <exception cref="T:System.IO.IOException">An I/O error occurs.</exception>
       </Docs>
     </Member>
     <Member MemberName="ReadBlock">
@@ -2250,7 +2250,7 @@ Following a call to <xref:System.IO.StreamReader.Close%2A>, any operations on th
         <exception cref="T:System.ArgumentOutOfRangeException">
           <paramref name="index" /> or <paramref name="count" /> is negative.</exception>
         <exception cref="T:System.ObjectDisposedException">The <see cref="T:System.IO.StreamReader" /> is closed.</exception>
-        <exception cref="T:System.IO.IOException">An I/O error occurred.</exception>
+        <exception cref="T:System.IO.IOException">An I/O error occurs.</exception>
       </Docs>
     </Member>
     <Member MemberName="ReadBlockAsync">