[NRBF] Reduce the most time-consuming test case to avoid timeouts for…

… checked builds (dotnet#110550)

src/libraries/System.Formats.Nrbf/tests/ArraySinglePrimitiveRecordTests.cs

@@ -20,7 +20,7 @@ public NonSeekableStream(byte[] buffer) : base(buffer) { }
 
     public static IEnumerable<object[]> GetCanReadArrayOfAnySizeArgs()
     {
-        foreach (int size in new[] { 1, 127, 128, 512_001, 512_001 })
+        foreach (int size in new[] { 1, 127, 128, 20_001 })
         {
             yield return new object[] { size, true };
             yield return new object[] { size, false };