Describe the bug
The automatic update script is currently failing on an M1 / arm64 Mac with the reason 'unsupported architecture'.

Your version of Talisman is outdated. Updating Talisman to v1.27.0
Talisman currently only supports x86 and x86_64 architectures.
If this is a problem for you, please open an issue: https://github.com/thoughtworks/talisman/issues/new
/tmp/update_talisman.bash: line 97: E_UNSUPPORTED_ARCH: unbound variable

To Reproduce

1. Install on an M1 Mac
2. Wait until an update is released
3. Attempt to use Talisman (perform a commit with the pre-commit hook enabled, etc), which will trigger the automatic update check

Expected Behaviour
arm64 should be recognised and the update should work

Additional Context
In #356 (commit 3184dac ) support was added to the Talisman install script for arm64, which works successfully. I suspect the update_talisman.sh script also needs a similar fix applied to add arm64 to the allowed list.