docs: fixing example action usage in readme

[pauldotyu]

The pinned versions of docker and trivy actions were resulting in "An action could not be found at the URI" errors.

[sozercan]

@pauldotyu where are you getting this error? ideally we want to use pinned hashes instead of mutable tags

[pauldotyu]

@pauldotyu where are you getting this error? ideally we want to use pinned hashes instead of mutable tags

I spun up a test repo on GH and copy-pasted the sample workflow from the README and the workflow run resulted in the following error:

Error: An action could not be found at the URI 'https://api.github.com/repos/aquasecurity/trivy-action/tarball/465a07811f14bebb1938fbed4728c6a1ff8901fc' (E4C1:5301:103E0D:1DDBF4:6505F51D)

Updating to a recent version of the action is what made it work, so maybe we just need to pin to a later hash?

[sozercan]

@pauldotyu yea looks like that commit is not found: https://github.com/aquasecurity/trivy-action/commit/465a07811f14bebb1938fbed4728c6a1ff8901fc

updating to latest commit sgtm and please make sure to sign the DCO. Thanks!