Make the test more consistent

spec/type-compat.test.sh

@@ -23,14 +23,14 @@ echo "$s|$i|$j"

### append in arith context
declare s
(( s=1 ))
(( s+=2 ))  # arith add
(( s='1 '))
(( s+=' 2 '))  # arith add
declare -i i
(( i=1 ))
(( i+=2 ))
(( i='1 ' ))
(( i+=' 2 ' ))
declare -i j
(( j=x ))  # treated like zero
(( j+=2 ))
(( j='x ' ))  # treated like zero
(( j+=' 2 ' ))
echo "$s|$i|$j"
# stdout: 3|3|2