Fix lint and type-check errors in uboot test fixture

Fix import sorting (ruff I001) and replace pytest.fail() with
raise AssertionError to satisfy ty's call-non-callable check.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mangelajo

python/packages/jumpstarter-driver-uboot/jumpstarter_driver_uboot/driver_test.py

@@ -12,7 +12,6 @@
 from .driver import UbootConsole
 from jumpstarter.common.utils import serve
 
-
 UBOOT_RPM_URL = "https://kojipkgs.fedoraproject.org/packages/uboot-tools/2025.10/1.fc43/noarch/uboot-images-armv8-2025.10-1.fc43.noarch.rpm"
 
 
@@ -34,7 +33,7 @@ def uboot_image(tmpdir_factory):
                     downloaded += len(chunk)
             print(f"Downloaded {downloaded} bytes (expected {total})")
     except requests.RequestException as e:
-        pytest.fail(f"Failed to download u-boot RPM: {e}")
+        raise AssertionError(f"Failed to download u-boot RPM: {e}") from e
 
     print("Extracting u-boot.bin from RPM...")
     if shutil.which("rpm2cpio") and shutil.which("cpio"):