Resolve "The WebHook `recent_failures` counter may overflow"

What does this MR do?

Prevents WebHook#recent_failures from overflowing.

This is only necessary while the flag is as yet disabled - when it is enabled, the web-hook will never be executed. But for safety's sake, this still makes sense.

The maximum is set rather low (much lower than the actual maximum value of a smallint): this saves unnecessary DB updates.

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)

Related to #330817 (closed)