Fix duplication of "special:" in special workspace name

[Agent00Ming]

modified:   src/desktop/Workspace.cpp

Describe your PR, what does it fix/add?

Tokens for special workspaces have a duplicated special: string causing them to not spawn the windows properly.
(i.e. a special workspace called terminal would show up as special:special:terminal in the log)
Fixes #5726's special workspace spawning problems

Special workspaces always have a name that either: defaults to special when not specified on creation or must have special: prepended to their name when setting workspace rules.

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

I don't know where else this getConfigName() function is called so I don't know if it breaks something else.
Did a search through the project and it seems that KeybindManager.cpp is the only place where it is called as is. From my testing, movetoworkspace and its variants are all fine, togglespecialworkspace is also fine and workspace does not apply to special workspaces.

Is it ready for merging, or does it need work?

Ready for merging

[Agent00Ming]

Addendum: lines 256..271 of MiscFunctions.cpp:

int getWorkspaceIDFromString(const std::string& in, std::string& outName) {
    int result = WORKSPACE_INVALID;
    if (in.starts_with("special")) {
        outName = "special";

        if (in.length() > 8) {
            const auto NAME = in.substr(8);

            const auto WS = g_pCompositor->getWorkspaceByName("special:" + NAME);

            outName = "special:" + NAME;

            return WS ? WS->m_iID : g_pCompositor->getNewSpecialID();
        }

        return SPECIAL_WORKSPACE_START;

this is where the logic of resolving workspace names/IDs resides and where the other instance of special: is prepended to a special workspace's name