SDL: Updated copyright date

From 64c40b90282d787cc372eec2a822e18cf807cb3b Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Fri, 4 Jun 2021 14:34:21 -0700
Subject: [PATCH] Updated copyright date

---
 test/checkkeysthreads.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/checkkeysthreads.c b/test/checkkeysthreads.c
index 1d6c13a68..4019a80a3 100644
--- a/test/checkkeysthreads.c
+++ b/test/checkkeysthreads.c
@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2021 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages