fix wrong typo

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>
diff --git a/tests/opt-testcases/tls13-misc.sh b/tests/opt-testcases/tls13-misc.sh
index 635e31a..572a291 100755
--- a/tests/opt-testcases/tls13-misc.sh
+++ b/tests/opt-testcases/tls13-misc.sh
@@ -505,6 +505,6 @@
          "$G_NEXT_CLI localhost --priority=NORMAL:-VERS-ALL:+VERS-TLS1.3:+GROUP-ALL -d 10 -r --earlydata $EARLY_DATA_INPUT" \
          1 \
          -s "ClientHello: early_data(42) extension exists."                     \
-         -s "EncryptedExtensions: early_data(42) extension does not exists."    \
+         -s "EncryptedExtensions: early_data(42) extension does not exist."    \
          -s "NewSessionTicket: early_data(42) extension does not exist."        \
          -s "Last error was: -29056 - SSL - Verification of the message MAC failed"