lib: constants: change DEPOT_TOOLS_DIR to Path

BUG=None
TEST=CQ passes

Change-Id: I561b931a4aead9c9b313315a2ca3daf4f1cc0b81
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4374323
Reviewed-by: Lizzy Presland <zland@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_sdk.py b/scripts/cros_sdk.py
index e514876..9459208 100644
--- a/scripts/cros_sdk.py
+++ b/scripts/cros_sdk.py
@@ -186,7 +186,7 @@
 
     # Pass in the path to the depot_tools so that users can access them from
     # within the chroot.
-    cmd += ["DEPOT_TOOLS=%s" % constants.DEPOT_TOOLS_DIR]
+    cmd += [f"DEPOT_TOOLS={constants.DEPOT_TOOLS_DIR}"]
 
     return cmd