Same tag different case on two pages causes an error #1364

Describe the bug
If you create two pages and put the same tag, but with different casing on each one, the second one will break and not be able to be created.

To Reproduce
Steps to reproduce the behavior:

1. Create a new page and add a tag
2. Create another new page and add the same tag but use different capitalization
3. When you click "Create" it will error and you will no longer be able to access the page

Expected behavior
The page gets created with no errors.

I would expect case to be normalized if it will cause an issue to have two different casings

Screenshots
N/A

Host Info (please complete the following information):

• OS: Windows Server 2012 R2
• Wiki.js version: 2.0.12
• Database engine: MS SQL Server 2016

Additional context
N/A