fix(auth): Azure DevOps az-CLI token acquisition returns None on undecodable output (#3527)

_acquire_via_az_cli runs 'az account get-access-token' with text=True, so
subprocess.run decodes stdout with the locale encoding and raises
UnicodeDecodeError (a ValueError sibling, NOT a JSONDecodeError) when the output
can't be decoded. That escaped the except (OSError, TimeoutExpired,
JSONDecodeError, KeyError) tuple and crashed a helper whose contract is to
return str | None. Add UnicodeDecodeError to the tuple.

Test patches subprocess.run to raise UnicodeDecodeError and asserts resolve_token
returns None (fails before: the error propagated).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/specify_cli/authentication/azure_devops.py

@@ -76,7 +76,17 @@ class AzureDevOpsAuth(AuthProvider):
             payload = _json.loads(result.stdout)
             token = payload.get("accessToken", "").strip()
             return token or None
-        except (OSError, subprocess.TimeoutExpired, _json.JSONDecodeError, KeyError):
+        except (
+            OSError,
+            subprocess.TimeoutExpired,
+            _json.JSONDecodeError,
+            UnicodeDecodeError,
+            KeyError,
+        ):
+            # UnicodeDecodeError: text=True decodes az stdout with the locale
+            # encoding, which raises (not a JSONDecodeError) if the output isn't
+            # decodable — this helper's contract is to return None on any
+            # failure, never to propagate.
             return None
 
     @staticmethod