fix(presets): helpers:githubDigestChangelogs should only apply to Git digest updates (#39995)

Otherwise we'll incorrectly match on i.e.

https://github.com/nginx/nginx/compare/sha256:6697f8bc5fbb0a0e38f10f90cef119892bb1b5f10d61d17949027583c0eec73f..sha256:e8d62a25409b03ae4a10beb101bb937682f8d311f747e8feee362edff24c81d9

Author: jamietanna

lib/config/presets/internal/helpers.ts

@@ -27,6 +27,12 @@ export const presets: Record<string, Preset> = {
     packageRules: [
       {
         changelogUrl: '{{sourceUrl}}/compare/{{currentDigest}}..{{newDigest}}',
+        matchDatasources: [
+          'git-refs',
+          'git-tags',
+          'github-releases',
+          'github-tags',
+        ],
         matchSourceUrls: ['https://github.com/**'],
         matchUpdateTypes: ['digest'],
       },