Use min skill level on Vocation::getReqSkillTries

[ramon-bernardo]

Pull Request Prelude

• I have followed proper The Forgotten Server code styling.
• I have read and understood the contribution guidelines before making this PR.
• I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

• Use min skill level on Vocation::getReqSkillTries

#3721

[ramon-bernardo]

We have a problem here.

• Change MINIMUM_SKILL_LEVEL to 1.
• Create player with skill level 9 or below 10.
• Kill the player.
• An incorrect value is saved in db, because of std::pow(skillMultipliers[skill], static_cast<int32_t>(9 - 11)).
• skillMultipliers[skill] ^ -2

This must be merged for MINIMUM_SKILL_LEVEL to work correctly.