Static checks: introduce usage of "avocado-static-checks" project

This enables the bare minimum of the avocado-static-checks usage, adds
the submodule switches the "isort" check, one of the most simplistic,
to the one provided by the avocado-static-checks repo.

Signed-off-by: Cleber Rosa <[email protected]>

.github/workflows/ci.yml

@@ -19,6 +19,7 @@ jobs:
         with:
           fetch-depth: 0
           ref: ${{ github.event.pull_request.head.sha }}
+          submodules: true
       - name: Allow git to operate on directory checked out by GH Actions
         run: git config --global --add safe.directory `pwd`
       - name: Installing Avocado development dependencies

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "static-checks"]
+	path = static-checks
+	url = https://github.com/avocado-framework/avocado-static-checks

selftests/check.py

@@ -597,6 +597,9 @@ def create_suites(args):  # pylint: disable=W0621
     if args.dict_tests["static-checks"]:
         config_check_static = copy.copy(config_check)
         config_check_static["resolver.references"] = glob.glob("selftests/*.sh")
+        config_check_static["resolver.references"].append(
+            "static-checks/check-import-order"
+        )
         suites.append(TestSuite.from_config(config_check_static, "static-checks"))
 
     # ========================================================================