Bug 1807864

Description of problem:

Based on https://cloud.google.com/sdk/docs/quickstart-redhat-centos, I've added a *.repo definition that looks like this:

```
[google-cloud-sdk]
name=Google Cloud SDK
baseurl=https://packages.cloud.google.com/yum/repos/cloud-sdk-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg
       https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
```

The multi-line gpgkey entry is correctly handled by dnf, but PackageKit joins the strings with ';' and attempts to download the keys from this URL https://packages.cloud.google.com/yum/doc/yum-key.gpg;https:/packages.cloud.google.com/yum/doc/rpm-package-key.gpg getting a 404.

Even if the repo definition is buggy, I would expect PackageKit to be consistent with what dnf/yum do.


Version-Release number of selected component (if applicable):

PackageKit-1.1.12-3.el8.x86_64


How reproducible:
always


Steps to Reproduce:
1. add a repo definition like above
2. pkgcon get-updates
3.

Actual results:

Observing this in the terminal:
Fatal error: Failed to download gpg key for repo 'google-cloud-sdk': Status code: 404 for https://packages.cloud.google.com/yum/doc/yum-key.gpg;https:/packages.cloud.google.c│Feb 27 06:50:27 rhel-8-devel PackageKit[1744]: get-repo-list transaction /2_aaadcaad from uid 0 finished with success after 4ms
om/yum/doc/rpm-package-key.gpg


Additional info:

Is the repo definition buggy? https://dnf.readthedocs.io/en/latest/conf_ref.html#list-label states a list is one or more strings separated with comma or space characters, so as long as newline is treated as a space it seems ok.