improve concurrency of GitHub Actions

This will allow you to cancel older running actions for the current PR /
branch. This saves you some resources, but more importantly hopefully
frees up some spots in the queue a bit faster.

Saw this on the Node.js repo: nodejs/node#42017

.github/workflows/main.yml

@@ -2,6 +2,10 @@ name: CI
 
 on: [push]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
 env:
   NODE_VERSION: 12.x
 

.github/workflows/release-insiders.yml

@@ -4,6 +4,10 @@ on:
   push:
     branches: [main]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
 jobs:
   build:
     runs-on: ubuntu-latest