GHA: security updates (#46)

Author: vszakats

.github/workflows/c.yml

@@ -1,16 +1,22 @@
 name: Ubuntu
 
-on: [push]
+'on': [push]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.sha }}
+  cancel-in-progress: true
+
+permissions: {}
 
 jobs:
   build:
-
+    name: 'build'
     runs-on: ubuntu-latest
-    
     steps:
-    - uses: actions/checkout@v1
-    - name: install libcurl
-      run: sudo apt-get install libcurl4-openssl-dev
-    - name: make
-      run: make
-  
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          persist-credentials: false
+      - name: install libcurl
+        run: sudo apt-get install libcurl4-openssl-dev
+      - name: make
+        run: make