test: release SPI handle after panda enumeration

panda/python/__init__.py

@@ -345,10 +345,12 @@ class Panda:
 
   @classmethod
   def spi_list(cls):
-    _, _, serial, _ = cls.spi_connect(None)
-    if serial is not None:
-      return [serial, ]
-    return []
+    _, handle, serial, _ = cls.spi_connect(None)
+    try:
+      return [serial, ] if serial is not None else []
+    finally:
+      if handle is not None:
+        handle.close()
 
   def reset(self, enter_bootstub=False, enter_bootloader=False, reconnect=True):
     if enter_bootstub or enter_bootloader:

panda/python/dfu.py

@@ -87,13 +87,17 @@ class PandaDFU:
 
   @staticmethod
   def spi_list() -> list[str]:
+    handle = None
     try:
-      _, h = PandaDFU.spi_connect(None)
-      if h is not None:
-        dfu_serial = PandaDFU.st_serial_to_dfu_serial(h.get_uid(), h.get_mcu_type())
+      _, handle = PandaDFU.spi_connect(None)
+      if handle is not None:
+        dfu_serial = PandaDFU.st_serial_to_dfu_serial(handle.get_uid(), handle.get_mcu_type())
         return [dfu_serial, ]
     except PandaSpiException:
       pass
+    finally:
+      if handle is not None:
+        handle.close()
     return []
 
   @staticmethod