GitHub Action example configuration fails because `cargo-audit` not found

I set up a basic GitHub Action attempting to run the Salus scanner, via this PR: https://github.com/underdog-tech/dependabot-alert-bot/pull/13

The action file is copied/pasted directly from the examples, with the exception of the `actions/checkout` version and what triggers cause it to run.

This action is failing with the following:

```
reports:
- uri: file://salus-report.json
format: json
verbose: true
Calling `DidYouMean::SPELL_CHECKERS.merge!(error_name => spell_checker)' has been deprecated. Please call `DidYouMean.correct_error(error_name, spell_checker)' instead.
[INFORMATIONAL: 2023-03-28 15:52:15 +0000]: Salus is running.
# terminated with exception (report_on_exception is true):
/usr/local/lib/ruby/3.2.0/open3.rb:222:in `spawn': No such file or directory - cargo-audit (Errno::ENOENT)
from /usr/local/lib/ruby/3.2.0/open3.rb:222:in `popen_run'
from /usr/local/lib/ruby/3.2.0/open3.rb:103:in `popen3'
from /usr/local/lib/ruby/3.2.0/open3.rb:290:in `capture3'
from /home/lib/salus/scanners/base.rb:149:in `run_shell'
from /home/lib/salus/scanners/cargo_audit.rb:65:in `version'
from /home/lib/salus/scanners/base.rb:[34](https://github.com/underdog-tech/dependabot-alert-bot/actions/runs/4544749565/jobs/8011940142#step:4:35):in `initialize'
from /home/lib/salus/processor.rb:106:in `new'
from /home/lib/salus/processor.rb:106:in `block (2 levels) in run_scanner'
bundler: failed to load command: /home/bin/salus (/home/bin/salus)
/usr/local/lib/ruby/3.2.0/open3.rb:222:in `spawn': No such file or directory - cargo-audit (Errno::ENOENT)
from /usr/local/lib/ruby/3.2.0/open3.rb:222:in `popen_run'
from /usr/local/lib/ruby/3.2.0/open3.rb:103:in `popen3'
from /usr/local/lib/ruby/3.2.0/open3.rb:290:in `capture3'
from /home/lib/salus/scanners/base.rb:149:in `run_shell'
from /home/lib/salus/scanners/cargo_audit.rb:65:in `version'
from /home/lib/salus/scanners/base.rb:34:in `initialize'
from /home/lib/salus/processor.rb:106:in `new'
from /home/lib/salus/processor.rb:106:in `block (2 levels) in run_scanner'
```

It appears that this is expecting the `cargo-audit` command to always be present on the system, which is not the case for a default `ubuntu-latest` image, and certainly not the case for a Go-based project.