--assignee "Unassigned" picks wrong user

**Describe the bug**

Running:

jira issue edit --no-input --assignee "Unassigned"

should set assignee to "Unassigned" but it get set to another user, "Unassigned " instead.

The former doesn't have an email (apparently?) so there is no workaround.

1. JiraCLI Version:
```
(Version="1.3.0", GitCommit="ed84fe74f68ba1b2cf0504a931ca09a03b2c9fed", CommitDate="2023-01-02T09:59:32+00:00", GoVersion="go1.19.4", Compiler="gc", Platform="linux/amd64")

```

2. Are you using Jira cloud or on-premise jira server?
```
onprem
SERVER INFO
-----------

Version: 8.20.5
Build Number: 820005
Deployment Type: Server
Default Locale:

```

3. What operating system are you using? Also mention version.
```
linux centos 7
```

4. What terminal are you using? Also mention version.
```
gnome-terminal
```