fix(typescript): convert workers/pr/changelog to ts (#4888)

lib/workers/pr/changelog/common.ts

lib/workers/pr/changelog/hbs-template.ts

lib/workers/pr/changelog/index.ts

lib/workers/pr/changelog/release-notes.ts

lib/workers/pr/changelog/releases.ts

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

lib/workers/pr/pr-body.js

package.json

test/util.ts

test/workers/pr/__snapshots__/index.spec.ts.snap

test/workers/pr/changelog/__snapshots__/index.spec.ts.snap

...ers/pr/changelog/__snapshots__/release-notes.spec.ts.snap

.../workers/pr/changelog/__snapshots__/releases.spec.ts.snap

test/workers/pr/changelog/index.spec.ts

test/workers/pr/changelog/release-notes.spec.ts

test/workers/pr/changelog/releases.spec.ts

test/workers/pr/index.spec.ts

yarn.lock