test_git.sh: declare restore_opts and assign separately

This avoids masking return values. Fixes SC2155. Part of #891.

Author: rul

test_git.sh

@@ -908,7 +908,8 @@ function run_test() {
     shift
 
     declare -g "$retvar"
-    local restore_opts=$(set +o)
+    local restore_opts
+    restore_opts=$(set +o)
     set +o errexit
     set +o nounset
     set +o pipefail