Fix two minor typos

ci/compat.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
-# This script checks that `zig build` will return an useful error message when
+# This script checks that `zig build` will return a useful error message when
 # the Zig compiler is not compatible, instead of failing due to a syntax error.
 #
 # This script should be run on an UNIX system.

exercises/064_builtins.zig

@@ -58,7 +58,7 @@ pub fn main() void {
     // There is a difference between
     //  - a value, that overflowed at some point and is now corrupted
     //  - a single operation that overflows and maybe causes subsequent errors
-    // In practise we usually notice the overflowed value first and have to work
+    // In practice we usually notice the overflowed value first and have to work
     // our way backwards to the operation that caused the overflow.
     //
     // If there was no overflow at all while adding 5 to a, what value would