tests: write-errors.sh: avoid portability issue with dash

* tests/misc/write-errors.sh: Use printf rather than echo
since the echo builtin in dash will interpret backslashes.
* tests/misc/read-errors.sh: Likewise for consistency.

tests/misc/read-errors.sh

@@ -20,7 +20,7 @@
 
 ! cat . >/dev/null 2>&1 || skip_ "Need unreadable directories"
 
-echo "\
+printf '%s' "\
 basenc --base32 .
 basenc -d --base64 .
 cat .

tests/misc/write-errors.sh

@@ -25,7 +25,7 @@ fi
 
 # Writers that may output data indefinitely
 # First word in command line is checked against built programs
-echo "\
+printf '%s' "\
 cat /dev/zero
 comm -z /dev/zero /dev/zero
 cut -z -c1- /dev/zero