feat(changelog): cache getTags requests per run

lib/workers/pr/changelog/source-github.ts

@@ -3,6 +3,7 @@ import { PLATFORM_TYPE_GITHUB } from '../../../constants/platforms';
 import { Release } from '../../../datasource';
 import { logger } from '../../../logger';
 import * as globalCache from '../../../util/cache/global';
+import * as runCache from '../../../util/cache/run';
 import * as hostRules from '../../../util/host-rules';
 import { GithubHttp } from '../../../util/http/github';
 import * as allVersioning from '../../../versioning';
@@ -12,7 +13,7 @@ import { addReleaseNotes } from './release-notes';
 
 const http = new GithubHttp();
 
-async function getTags(
+async function getTagsInner(
   endpoint: string,
   repository: string
 ): Promise<string[]> {
@@ -41,6 +42,21 @@ async function getTags(
   }
 }
 
+async function getTags(
+  endpoint: string,
+  repository: string
+): Promise<string[]> {
+  const cacheKey = `getTags-${endpoint}-${repository}`;
+  const cachedResult = runCache.get(cacheKey);
+  // istanbul ignore if
+  if (cachedResult !== undefined) {
+    return cachedResult;
+  }
+  const promisedRes = getTagsInner(endpoint, repository);
+  runCache.set(cacheKey, promisedRes);
+  return promisedRes;
+}
+
 export async function getChangeLogJSON({
   versioning,
   fromVersion,