gcom4 package: Revert the recent change to Github git clone address

[penguian]

Martin Dix reported that the change due to pull request #155 breaks the git clone command for gcom4 by asking for a password.

==> Installing gcom4-git.2024.05.28=access-esm1.5-7xql2zmt54bnvdgzalcc44joachmby56 [8/15]
==> No binary for gcom4-git.2024.05.28=access-esm1.5-7xql2zmt54bnvdgzalcc44joachmby56 found: installing from source
Username for 'https://github.com/'

Revert the change

git = "https://github.com/ACCESS-NRI/GCOM4.git"

back to

git = "git@github.com:ACCESS-NRI/GCOM4.git"