ci: abort redundant PR builds (#40)

* ci: abort redundant PR builds

* bump checkouts

.github/workflows/ci.yml

@@ -6,6 +6,10 @@ on:
   pull_request:
   workflow_dispatch:
 
+concurrency: # Cancel stale PR builds (but not push builds)
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: true
+
 jobs:
   build:
     strategy:
@@ -30,7 +34,7 @@ jobs:
             shell: bash
           - target:
               os: macos
-            builder: macos-10.15
+            builder: macos-12
             shell: bash
           - target:
               os: windows
@@ -43,10 +47,10 @@ jobs:
 
     name: '${{ matrix.target.os }}-${{ matrix.target.cpu }} (Nim ${{ matrix.branch }})'
     runs-on: ${{ matrix.builder }}
-    continue-on-error: ${{ matrix.branch == 'version-1-6' || matrix.branch == 'devel' }}
+    continue-on-error: ${{ matrix.branch == 'devel' }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
         with:
           submodules: true
 
@@ -103,7 +107,6 @@ jobs:
         if: >
           steps.windows-dlls-cache.outputs.cache-hit != 'true' &&
           runner.os == 'Windows'
-        shell: bash
         run: |
           mkdir -p external
           curl -L "https://nim-lang.org/download/windeps.zip" -o external/windeps.zip
@@ -112,9 +115,8 @@ jobs:
       - name: Path to cached dependencies (Windows)
         if: >
           runner.os == 'Windows'
-        shell: bash
         run: |
-          echo '${{ github.workspace }}'"/external/dlls-${{ matrix.target.cpu }}" >> $GITHUB_PATH
+          echo "${{ github.workspace }}/external/dlls-${{ matrix.target.cpu }}" >> $GITHUB_PATH
 
       - name: Derive environment variables
         run: |
@@ -143,8 +145,7 @@ jobs:
           echo "ncpu=$ncpu" >> $GITHUB_ENV
           echo "MAKE_CMD=${MAKE_CMD}" >> $GITHUB_ENV
 
-      - name: Build Nim and associated tools
-        shell: bash
+      - name: Build Nim and Nimble
         run: |
           curl -O -L -s -S https://raw.githubusercontent.com/status-im/nimbus-build-system/master/scripts/build_nim.sh
           env MAKE="${MAKE_CMD} -j${ncpu}" ARCH_OVERRIDE=${PLATFORM} NIM_COMMIT=${{ matrix.branch }} \
@@ -153,9 +154,8 @@ jobs:
           echo '${{ github.workspace }}/nim/bin' >> $GITHUB_PATH
 
       - name: Run tests
-        shell: bash
         run: |
           nim --version
           nimble --version
           nimble install -y --depsOnly
-          env NIMLANG="c" nimble test
+          env NIMLANG=c nimble test