Move luacheck to a separate pipeline

luacheck doesn't depend on Tarantool version and it is
more than enough to run it once. Moreover it doesn't block
testing now in case of missed warnings.

.github/workflows/check_on_push.yaml

@@ -0,0 +1,25 @@
+name: Run static analysis
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  run-static-analysis:
+    if: |
+      github.event_name == 'push' ||
+      github.event_name == 'pull_request' && github.event.pull_request.head.repo.full_name != github.repository
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+
+    - name: Setup Tarantool
+      uses: tarantool/setup-tarantool@v1
+      with:
+        tarantool-version: '2.6'
+
+    - name: Setup luacheck
+      run: tarantoolctl rocks install luacheck 0.25.0
+
+    - name: Run luacheck
+      run: .rocks/bin/luacheck .

.github/workflows/test_on_push.yaml

@@ -39,9 +39,6 @@ jobs:
       - name: Stop Mono server
         run: sudo kill -9 $(sudo lsof -t -i tcp:8084) || true
 
-      - name: Run linter
-        run: .rocks/bin/luacheck .
-
       - name: Run tests
         run: .rocks/bin/luatest -v
 
@@ -71,8 +68,5 @@ jobs:
       - name: Stop Mono server
         run: sudo kill -9 $(sudo lsof -t -i tcp:8084) || true
 
-      - name: Run linter
-        run: .rocks/bin/luacheck .
-
       - name: Run tests
         run: .rocks/bin/luatest -v