Scan github ssh repositories fail in docker image.

[JeroenKnoops]

When using the docker container, scanning a github repository with ssh fails.

Example error:

Example from a spdx-builder scan:

License scanner tries to checkout: ssh://git%40github.com/FasterXML/jackson-bom.git.
You need a ssh key associated with a github account in order to clone this repo.

2021-02-11 08:19:24.814  INFO 1 --- [ctionExecutor-2] c.p.r.l.core.domain.LicenseInteractor    : Scan pkg:maven/com.fasterxml.jackson/jackson-bom@2.12.1 from git+ssh://git%40github.com/FasterXML/jackson-bom.git@jackson-bom-2.12.1
2021-02-11 08:19:24.815  INFO 1 --- [ctionExecutor-2] c.p.r.l.c.domain.download.DownloadCache  : Create cache for git+ssh://git%2540github.com/FasterXML/jackson-bom.git@jackson-bom-2.12.1
2021-02-11 08:19:24.817  INFO 1 --- [ctionExecutor-2] c.p.r.l.c.domain.download.DownloadCache  : Claim #1 of cache for git+ssh://git%2540github.com/FasterXML/jackson-bom.git@jackson-bom-2.12.1
2021-02-11 08:19:24.819  INFO 1 --- [ctionExecutor-2] c.p.r.l.core.command.ShellCommand        : Invoke git [clone, --depth=1, ssh://git%40github.com/FasterXML/jackson-bom.git, --branch, jackson-bom-2.12.1, /tmp/licenses-7126875473084991774/18f3044d-9c1a-4784-970b-e6180ed1530a] from /tmp/licenses-7126875473084991774/18f3044d-9c1a-4784-970b-e6180ed1530a
Cloning into '/tmp/licenses-7126875473084991774/18f3044d-9c1a-4784-970b-e6180ed1530a'...
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.