ci: use concurrency to cancel redundant in‑flight runs

Use the concurrency feature to cancel any in‑progress run before
starting the next one, so only the latest CI run executes; all earlier
ones get canceled

Signed-off-by: Ruowen Qin <ruowenq2@illinois.edu>

Author: chinrw

.github/workflows/meson.yml

@@ -1,4 +1,9 @@
 name: Meson Build and Test
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref_name }}
+  cancel-in-progress: true
+
 on:
   push:
     branches: [main, ci]

.github/workflows/nix.yml

@@ -1,4 +1,9 @@
 name: Meson Build and Test via nix
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref_name }}
+  cancel-in-progress: true
+
 on:
   push:
     branches: [main, ci]