[semver:patch] allow tag deployments by using full path refs

[a14m]

This edit is just more verbose about which reference is being pushed and to which remote

<refspec>: If <dst> doesn’t start with refs/ (e.g. refs/heads/master)
we will try to infer where in refs/* on the destination <repository> it belongs based on
the type of <src> being pushed and whether <dst> is ambiguous.
If <dst> unambiguously refers to a ref on the <repository> remote, then push to that ref.

Ref: https://mirrors.edge.kernel.org/pub/software/scm/git/docs/git-push.html

The added benefit of this edit is that we can now deploy both branches and tags based on the definition of the parameters.branch

ex:

• refs/heads/master will always deploy the master branch
• $CIRCLE_BRANCH is the same default behavior as now
• refs/heads/$CIRCLE_BRANCH is the same default behavior now (same as the previous version)
• refs/tags/$CIRCLE_TAG is a "hacky" way for deploying tags to Heroku

Fixes: #7
Safer than #8

As when a new repo is created on heroku, the command used in
#8 would fail with the following error

hint: The <src> part of the refspec is a commit object.
hint: Did you mean to create a new branch by pushing to
hint: 'v2.0.0^{}:refs/heads/master'?

Backward compatible but the naming of the variable could be changed in a later release to indicate that it's taking a reference path to deploy on the refs/heads/main heroku branch

[gmemstr]

We're opting to use #8, as it's a nicer end-user experience for the orb.