Fix sync writing of hstore values (npgsql#5452)

fixes npgsql#5445

(cherry picked from commit b21c41c)
Signed-off-by: monjowe <jonas.westman@monitor.se>

src/Npgsql/Internal/Converters/HstoreConverter.cs

@@ -147,7 +147,7 @@ async ValueTask Write(bool async, PgWriter writer, T value, CancellationToken ca
                 if (async)
                     await writer.WriteCharsAsync(kv.Value.AsMemory(), _encoding, cancellationToken).ConfigureAwait(false);
                 else
-                    writer.WriteChars(kv.Key.AsSpan(), _encoding);
+                    writer.WriteChars(kv.Value.AsSpan(), _encoding);
             }
             i += 2;
         }