Add CI concurrency control and fail-fast

- Add concurrency group to cancel in-progress builds when new commit pushed
- Change postgres matrix fail-fast to true

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: oyvindberg

.github/workflows/build.yml

@@ -6,6 +6,10 @@ on:
   pull_request:
     branches: [ 'main' ]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   scalafmt:
     timeout-minutes: 10
@@ -70,7 +74,7 @@ jobs:
     timeout-minutes: 25
     if: "!contains(github.event.head_commit.message, 'ci skip')"
     strategy:
-      fail-fast: false
+      fail-fast: true
       matrix:
         postgres-version: [12, 16]
     steps: