chore: Setup build concurrency to reduce number of simultaneous builds on a PR

.github/workflows/build-pr.yml

@@ -1,5 +1,9 @@
 name: Earthly PR +build
 
+concurrency: 
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
 on:
   pull_request:
 

.github/workflows/build.yml

@@ -1,5 +1,9 @@
 name: Earthly main branch +all
 
+concurrency: 
+  group: ${{ github.workflow }}-main
+  cancel-in-progress: true
+
 on:
   workflow_dispatch:
   push: