Use backticks for shell portability w/ Solaris.

Author: daztucker

.github/run_test.sh

@@ -48,7 +48,7 @@ fi
 if [ "$1" = "dropbear-versions" ]; then
 	make regress-binaries
 	# Work backward from current version to last version we support.
-	for ver in master $(cd /tmp/dropbear && git tag | grep -E 'DROPBEAR_' | sort -rn); do
+	for ver in master `cd /tmp/dropbear && git tag | grep -E 'DROPBEAR_' | sort -rn`; do
 		year=$(echo "$ver" | cut -f2 -d_ | cut -f1 -d.)
 		if [ "$ver" != "master" ] && [ "$year" -lt "2020" ]; then
 			exit 0