Update DEVCTR_IMAGE_TAG to v91

The new devctr image contains new Python and Rust dependencies,
notably the Rust toolchain 1.96.0.

Signed-off-by: Marco Marangoni <mamarang@amazon.com>

Author: marco-marangoni

tools/devtool

@@ -68,7 +68,7 @@
 DEVCTR_IMAGE_NO_TAG="public.ecr.aws/firecracker/fcuvm"
 
 # Development container tag
-DEVCTR_IMAGE_TAG=${DEVCTR_IMAGE_TAG:-v90}
+DEVCTR_IMAGE_TAG=${DEVCTR_IMAGE_TAG:-v91}
 
 # Development container image (name:tag)
 # This should be updated whenever we upgrade the development container.