ukify: catch error when loading foreign pe file

The autodetection code is supposed to throw ValueError when it
cannot figure out the version so that we fall back to the next method.
With the patch:
  Kernel version not specified, starting autodetection 😖.
  Real-Mode Kernel Header magic not found
  + readelf --notes vmlinuz/arm64/vmlinuz-6.0.9-300.fc37.aarch64
  readelf: vmlinuz/arm64/vmlinuz-6.0.9-300.fc37.aarch64: Error: Not an ELF file - it has the wrong magic bytes at the start
  Found uname version: 6.0.9-300.fc37.aarch64

src/ukify/ukify.py

@@ -161,7 +161,10 @@ class Uname:
         ]
 
         print('+', shell_join(cmd))
-        notes = subprocess.check_output(cmd, text=True)
+        try:
+            notes = subprocess.check_output(cmd, stderr=subprocess.PIPE, text=True)
+        except subprocess.CalledProcessError as e:
+            raise ValueError(e.stderr.strip()) from e
 
         if not (m := re.search(cls.NOTES_PATTERN, notes, re.MULTILINE)):
             raise ValueError('Cannot find Linux version note')