Make dependabot ignore libp2p libs (#6018)

## Motivation

libp2p/go-libp2p#2793 broke observed address handling and consequently routing discovery mechanism, too.
This is not the first time we're having problems because of (semi-)automatic libp2p dependency updates.
Prerequisite for re-enabling automatic updates of libp2p libs: QUIC and routing discovery systests

.github/dependabot.yml

@@ -4,6 +4,12 @@ updates:
     directory: "/"
     schedule:
       interval: "daily"
+    ignore:
+      # Following cutting edge releases of libp2p is risky.
+      # Latest problem fixed here: https://github.com/libp2p/go-libp2p/pull/2825
+      # We need QUIC and routing discovery systest cases before we can re-enable
+      # dependabot for libp2p
+      - dependency-name: github.com/libp2p/*
 
   - package-ecosystem: "github-actions"
     directory: "/"