Update tools/dep_updaters/update-test426-fixtures.sh

Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: Trott

tools/dep_updaters/update-test426-fixtures.sh

@@ -21,4 +21,6 @@ TMP_FILE=$(mktemp)
 sed "s#https://github.com/tc39/source-map-tests/commit/[0-9a-f]*#https://github.com/tc39/source-map-tests/commit/$SHA#" "$README" > "$TMP_FILE"
 mv "$TMP_FILE" "$README"
 
-echo "test426 fixtures updated to $SHA."
+# The last line of the script should always print the new version,
+# as we need to add it to $GITHUB_ENV variable.
+echo "NEW_VERSION=$SHA"