This GitHub Action sets a pull request status to pending if the title includes "WIP".
An example workflow looks like this (switch to the <> Edit new file tab when creating a new workflow and paste the code below):
on: [pull_request]
name: "Set status on pull_request"
jobs:
wip:
name: "Set status"
runs-on: ubuntu-latest
steps:
- uses: wip/action@master