docs: update references to bfra-me/renovate-config to v1.7.15 (#552)

Co-authored-by: bfra-me[bot] <118100583+bfra-me[bot]@users.noreply.github.com>

README.md

@@ -16,7 +16,7 @@ This repository contains [Renovate](https://renovatebot.com/) configuration pres
 
 ```json
 {
-  "extends": ["github>bfra-me/renovate-config#v1.7.14"]
+  "extends": ["github>bfra-me/renovate-config#v1.7.15"]
 }
 ```
 
@@ -26,7 +26,7 @@ To reuse the workflow from this repository, add it to your GitHub Actions workfl
 
 ```yaml
 - name: Renovate
-  uses: bfra-me/renovate-config/.github/workflows/[email protected].14
+  uses: bfra-me/renovate-config/.github/workflows/[email protected].15
   with:
     dry_run: false
     renovate_git_author: 'fro-bot[bot] <109017866+fro-bot[bot]@users.noreply.github.com>'