TASK: Correct typos in StyleAndUsage.rst

[Safat99]

spelling mistakes found and corrected

Upgrade instructions

Review instructions

Checklist

• Code follows the PSR-2 coding style
• The PR is created against the lowest maintained branch
• Tests have been created, run and adjusted as needed
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[jonnitto]

@Safat99, thank you for your PR! I leaved a comment on one thing, who should be changed.

[jonnitto]

And I also think, the correct branch for this would be 8.3

[Safat99]

Do I need to change or push it to the 8.3 branch?

[kitsunet]

@Safat99 Unfortunately I think you will have to cherry-pick to this to 8.3 and force push the PR branch, as just changing in Github would apply all other changes of 9.0 to the 8.3 branch as well.