T4 strains do not take up a T4 slot

[Wisemonster]

Description

Title, T4s evoing to a strain frees up the T4 slot they were taking up, allowing another T4 to appear. This effectively means each T4 strain adds a T4 slot.

Test Merges

Server-Side Code Modifications: https://tgstation13.org/parsed-logs/sybil/server_side_modifications.dm

Round ID: 27731
BYOND Version: 515.1633
Server revision compiled on: 2024-07-01T00:05:53+00:00
Master commit: 7ef611ddd9b3ba7ad56e743ac3d2cf1a5fd54a3b
The following pull requests are currently test merged:
#16001: 'Boiler Tweaks' by Barnet2 at commit 01bfeb77c5
#15961: 'Opt-in squad radio TTS' by breadhunt at commit ae6aaa8dce
#16154: 'Adds Retrograde Sentinel Strain' by Notamaniac at commit d3b01c3331
#16082: 'Melee attacks no longer lock inputs' by Xander3359 at commit f1b9f0c981
#16165: 'Off-hand shooting' by Lumipharon at commit d3f7271a3f

Local commit: e76a753
Server tools version: 6.5.

Reproduction Steps

1. Be a T4 with a strain to swap to
2. Swap to that strain
3. Have another caste try to evo to the T4 you previously were
4. Watch as they successfully evo to that T4

Screenshots