scripts: compliance: add a check for MAINTAINERS.yml format

Add a compliance check that tries to load MAINTAINERS.yml with
get_maintainer.Maintainers() if it's been modified by the CL, and fail
compliance if it fails to be parsed.

Example output:

```
ERROR   : Test MaintainersFormat failed:
Error parsing MAINTAINERS.yml: MAINTAINERS.yml: YAML error: while
scanning a simple key
  in "MAINTAINERS.yml", line 976, column 1
could not find expected ':'
  in "MAINTAINERS.yml", line 977, column 3
```

```
ERROR   : Test MaintainersFormat failed:
Error parsing MAINTAINERS.yml: MAINTAINERS.yml: glob pattern
'drivers/regulator' in 'files' in area 'Drivers: Regulators' matches a
directory, but has no trailing '/'
```

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

scripts/ci/check_compliance.py

@@ -20,6 +20,9 @@ import shlex
 from junitparser import TestCase, TestSuite, JUnitXml, Skipped, Error, Failure
 import magic
 
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+from get_maintainer import Maintainers, MaintainersError
+
 logger = None
 
 def git(*args, cwd=None):
@@ -967,6 +970,27 @@ class ImageSize(ComplianceTest):
                              f"less than {limit >> 10}kB")
 
 
+class MaintainersFormat(ComplianceTest):
+    """
+    Check that MAINTAINERS file parses correctly.
+    """
+    name = "MaintainersFormat"
+    doc = "Check that MAINTAINERS file parses correctly."
+    path_hint = "<git-top>"
+
+    def run(self):
+        MAINTAINERS_FILES = ["MAINTAINERS.yml", "MAINTAINERS.yaml"]
+
+        for file in get_files(filter="d"):
+            if file not in MAINTAINERS_FILES:
+                continue
+
+            try:
+                Maintainers(file)
+            except MaintainersError as ex:
+                self.failure(f"Error parsing {file}: {ex}")
+
+
 def init_logs(cli_arg):
     # Initializes logging