Update asdf in CI actions to >=0.16.0. Add actions to dependabot update list.

[jadrian]

Summary of changes

Asana Ticket: none

Updates asdf-vm/actions/install to 4.0.1, which is the latest version and also supports asdf >= 0.16.0. (The actual latest version of asdf, which is always pulled by the install action, is currently 0.19.0.) Also adds dependabot updates of Github actions so that we keep up-to-date.

This addresses the following warning in the Credo step of Dev Tasks CI runs:

You have tried to upgrade to asdf 0.16.0 or newer. Versions 0.16.0 is a
complete rewrite of asdf in Go. This text is being printed by the older
Bash implementation. If you are seeing this you have not migrated to
asdf 0.16.0. Please follow the instructions on the upgrade guide to
migrate to the new version.

Aside from this notice, this older Bash implementation works as it did
in asdf version 0.15.0 and older.

Migration guide: https://asdf-vm.com/guide/upgrading-to-v0-16

Before: CI run before clearing asdf cache. In the "ASDF" job, the "ASDF cache" step shows a cache hit, so it skips installing asdf. Then in the "Dev Tasks" job, the "Credo" step uses the old version of asdf, and therefore shows the warning.

After: CI run after clearing asdf cache. In the "ASDF" job, the "ASDF cache" step has a cache miss, so the "Run asdf-vm/actions/install" step runs and installs the latest version of asdf. Then in the "Dev Tasks" job, the "Credo" step uses the new version of asdf, and we don't get the warning.