[TF2] Add vsh_ and zi_ game type identifiers to serverbrowsergametypes.txt

[orangy57]

The "simplified list" feature in the community server browser normally distinguishes the gamemode of official/community maps by checking the prefix of the map in servers/serverbrowsergametypes.txt. Since Versus Saxton Hale and Zombie Infection have been added to the official Casual rotation, they should be denoted in the community server browser when using the "simplified list" option.

This can be fixed by opening serverbrowsergametypes.txt and adding the following after line 57:

    "gametype_12"
    {
        "prefix"    "vsh_"
        "name"      "versus saxton hale"
    }
    "gametype_13"
    {
        "prefix"    "zi_"
        "name"      "zombie infection"
    }

Example:

[kisak-valve]

Partial duplicate of #5050. Let's use this issue report to focus on Zombie Infection.