feat: ignore unavailable users

lib/workers/pr/index.ts

@@ -37,6 +37,11 @@ async function addCodeOwners(
   return [...new Set(assigneesOrReviewers.concat(await codeOwnersForPr(pr)))];
 }
 
+function filterUnavailableUsers(users: string[]): string[] {
+  return users;
+  // TODO: Delegate filtering logic to platform.
+}
+
 export async function addAssigneesReviewers(
   config: RenovateConfig,
   pr: Pr
@@ -45,6 +50,7 @@ export async function addAssigneesReviewers(
   if (config.assigneesFromCodeOwners) {
     assignees = await addCodeOwners(assignees, pr);
   }
+  assignees = filterUnavailableUsers(assignees);
   if (assignees.length > 0) {
     try {
       assignees = assignees.map(noLeadingAtSymbol);
@@ -74,6 +80,7 @@ export async function addAssigneesReviewers(
   if (config.additionalReviewers.length > 0) {
     reviewers = reviewers.concat(config.additionalReviewers);
   }
+  reviewers = filterUnavailableUsers(reviewers);
   if (reviewers.length > 0) {
     try {
       reviewers = [...new Set(reviewers.map(noLeadingAtSymbol))];