Revert "gh: renovate: remove reference to old ipsec config file"

In commit f207c87, we erroneously
removed the reference to the ".github/actions/ipsec/configs.yaml" file,
given it was not used anymore in main. However, the renovate config also
manages stable branches, where the file is still present (v1.16).
This reverts commit f207c87.

Signed-off-by: Simone Magnani <simone.magnani@isovalent.com>

Author: smagnani96

.github/renovate.json5

@@ -25,6 +25,7 @@
     ".github/actions/ginkgo/**",
     ".github/actions/lvh-kind/**",
     ".github/actions/set-env-variables/action.yml",
+    ".github/actions/ipsec/configs.yaml",
     ".github/workflows/**",
     ".github/ISSUE_TEMPLATE/bug_report.yaml",
     "cilium-cli/**",