[ssl/ssl-certificate-expiry] Disable shellcheck SC1090

When linting this script, this will always fire. This is because shellcheck
only does static code analysis and thus can not determine the filepath.

References:
- https://www.shellcheck.net/wiki/SC1090

plugins/ssl/ssl-certificate-expiry

@@ -72,7 +72,7 @@ uncached updates after the cache file is older than an hour.
 
 =cut
 
-# shellcheck disable=SC1091
+# shellcheck disable=SC1090,SC1091
 . "${MUNIN_LIBDIR}/plugins/plugin.sh"
 
 if [ "${MUNIN_DEBUG:-0}" = 1 ]; then