fix(install): return right exit codes

As the main function was not the last command, it did always
return a zero status code. Exiting right after main allows us to
return the actual return code instead.

Analogous to anchore/syft#2664 .

Signed-off-by: Stefan Hacker <mail@hacst.net>

install.sh

@@ -695,5 +695,6 @@ set +u
 if [ -z "${TEST_INSTALL_SH}" ]; then
   set -u
   main "$@"
+  exit $?
 fi
-set -u
+set -u