tests: several -Wwrite-strings fixes.

test/checkkeys.c

@@ -137,9 +137,10 @@ PrintKey(SDL_Keysym * sym, SDL_bool pressed, SDL_bool repeat)
 }
 
 static void
-PrintText(char *eventtype, char *text)
+PrintText(const char *eventtype, const char *text)
 {
-    char *spot, expanded[1024];
+    const char *spot;
+    char expanded[1024];
 
     expanded[0] = '\0';
     for ( spot = text; *spot; ++spot )