fix: only-issue-types does not affect PRs (#1338)

* fix:  does not affect PRs

* docs: mention new behaviour specifically in README.md

* test: add new test case to avoid regression

* chore: run build

src/classes/issues-processor.ts

@@ -252,7 +252,7 @@ export class IssuesProcessor {
       return; // If the issue has an 'include-only-assigned' option set, process only issues with nonempty assignees list
     }
 
-    if (this.options.onlyIssueTypes) {
+    if (this.options.onlyIssueTypes && !issue.isPullRequest) {
       const allowedTypes = this.options.onlyIssueTypes
         .split(',')
         .map(t => t.trim().toLowerCase())