fix typo in 076 (sentinal -> sentinel)

exercises/076_sentinels.zig

@@ -53,7 +53,7 @@ pub fn main() void {
 
     // So now we have a zero-terminated array and a many-item
     // pointer that reference the same data: a sequence of
-    // numbers that both ends in and CONTAINS the sentinal value.
+    // numbers that both ends in and CONTAINS the sentinel value.
     //
     // Attempting to loop through and print both of these should
     // demonstrate how they are similar and different.