ci: Use Renovate to update GitHub actions

Compared to Dependabot Renovate:

* updates the versions of GitHub runners
* pins the version of actions

Author: Oleksandr Dzhychko

.github/dependabot.yml

@@ -24,11 +24,6 @@ updates:
     directory: "/model-server"
     schedule:
       interval: "daily"
-  - package-ecosystem: "github-actions"
-    open-pull-requests-limit: 20
-    directory: "/"
-    schedule:
-      interval: "daily"
   # We use the default versioning strategy for npm (increase for apps and widen for libraries),
   # so that clients are free to select an appropriate version from the allowed range, when they use one of the libraries.
   - package-ecosystem: "npm"

renovate.json5

@@ -12,5 +12,6 @@
     "pre-commit",
     "gradle-wrapper",
     "nvm",
+    "github-actions",
   ],
 }