Fix TestSuicideByHeldItem and TestSuicideByHeldItemSpreadDamage

[FluffMe]

About the PR

When Content.Shared.Atmos.Atmospherics.LowPressureDamage is set to anything other than 1 or 0 TestSuicideByHeldItem and TestSuicideByHeldItemSpreadDamage fail assertions of damage done.

With LowPressureDamage = 4

  Failed TestSuicideByHeldItemSpreadDamage [475 ms]
  Error Message:
     Assert.That(damageableComp.Damage.DamageDict["Slash"], Is.EqualTo(lethalDamageThreshold / 2))
  Expected: 100
  But was:  99

  Failed TestSuicideByHeldItem [955 ms]
  Error Message:
     Assert.That(damageableComp.Damage.DamageDict["Slash"], Is.EqualTo(lethalDamageThreshold))
  Expected: 200
  But was:  198

The tests are fine with Atmospherics.LowPressureDamage = 1 due to rounding up to next integer (199.5->200) which is why this issue was not spotted sooner.

I've noticed that tests fail only on full or expanded test runs.
Example: --filter SuicideCommandTests passes, --filter Commands fails.
The test player must take a tick of barotrauma damage at some point.

Healing all damage before running the command and the damage assertions fixes the issue.

Special thanks to @SlamBamActionman for tracking down the bug.

Why / Balance

Bug fix. Needed downstream due to changed low pressure damage.

Technical details

DamageableSystem.SetAllDamage() to 0 before running the commands and asserting the damage.

Media

N/A

Requirements

• I have read and am following the Pull Request and Changelog Guidelines.
• I have added media to this PR or it does not require an ingame showcase.

Breaking changes

N/A

Changelog
Not player facing

[lzk228]

god bless you

[Plykiya]

thanks for fixing my jank test

[slarticodefast]

Code looks good, thanks for the fix!