AgentProxyException when referencing a git repo in deps.edn

I'm trying to deploy a project that references another gitlab repo as a dependency through clojure deps.

In order to have the required ssh keys, I use the following custom buildpack on top of the clojure one: https://github.com/simon0191/custom-ssh-key-buildpack

But when trying to pull this private gitlab repo through clojure deps, I get the following message:

```
com.jcraft.jsch.agentproxy.AgentProxyException: connector is not available:
at com.jcraft.jsch.agentproxy.ConnectorFactory.createConnector (ConnectorFactory.java:120)
clojure.tools.gitlibs.impl$fn__1007.invokeStatic (impl.clj:30)
clojure.tools.gitlibs.impl/fn (impl.clj:28)
(...)
```

There seems to be some configuration that needs to be amended, but I can't find where.

Start by reproducing the private GitLab dependency fetch through deps.edn with the custom SSH-key buildpack. Inspect the clojure.tools.gitlibs.impl stack location at impl.clj:30 and the available SSH-agent configuration. Done means the dependency is fetched successfully without AgentProxyException.

Written by the indexing model from the issue text.