murano-agent requires Python '>=3.6' but the running Python is 2.7.17

I have installed disk-image-create, and then I run

$ git clone https://opendev.org/openstack/murano-agent.git
$ export ELEMENTS_PATH=murano-agent/contrib/elements
$ export DIB_CLOUD_INIT_DATASOURCES=OpenStack
$ disk-image-create vm ubuntu murano-agent -o ubuntu-murano-agent.qcow2

but it give the error:
2021-04-20 05:35:54.721 | Processing /opt/stack/murano-agent
2021-04-20 05:35:57.543 | murano-agent requires Python '>=3.6' but the running Python is 2.7.17
2021-04-20 05:35:57.809 | Unmount /tmp/dib_build.jM9ylGe5/mnt/var/cache/apt/archives
2021-04-20 05:35:57.824 | Unmount /tmp/dib_build.jM9ylGe5/mnt/tmp/in_target.d
2021-04-20 05:35:57.840 | Unmount /tmp/dib_build.jM9ylGe5/mnt/sys
2021-04-20 05:35:57.854 | Unmount /tmp/dib_build.jM9ylGe5/mnt/proc
2021-04-20 05:35:57.864 | Unmount /tmp/dib_build.jM9ylGe5/mnt/dev/pts
2021-04-20 05:35:57.874 | Unmount /tmp/dib_build.jM9ylGe5/mnt/dev
2021-04-20 05:35:58.100 | INFO diskimage_builder.block_device.blockdevice [-] State already cleaned - no way to do anything here

I run these under a virtual machine, and I do not have python2.7 installed, the python version is:
~$ python --version
Python 3.8.5

I have tried "alias python=python3" but without luck. Please help me with this problem, thanks!