refactor(github): Change github-related field types for repo cache

lib/modules/platform/github/pr.ts

@@ -12,7 +12,6 @@ function getPrApiCache(): ApiCache<GhPr> {
   const repoCache = getCache();
   repoCache.platform ??= {};
   repoCache.platform.github ??= {};
-  delete repoCache.platform.github.prCache;
   repoCache.platform.github.pullRequestsCache ??= { items: {} };
   const prApiCache = new ApiCache<GhPr>(
     repoCache.platform.github.pullRequestsCache as ApiPageCache<GhPr>,

lib/util/cache/repository/types.ts

@@ -144,7 +144,13 @@ export interface RepoCacheData {
     gitea?: {
       pullRequestsCache?: GiteaPrCacheData;
     };
-    github?: Record<string, unknown>;
+    github?: {
+      /**
+       * To avoid circular dependency problem, we use `unknown` type here.
+       */
+      pullRequestsCache?: unknown;
+      graphqlPageCache?: unknown;
+    };
     bitbucket?: {
       pullRequestsCache?: BitbucketPrCacheData;
     };