[LW] Log the type of failed validation

[Jolyon-S]

Goals (and why):
It is currently impossible to determine which endpoint failed validation from the safe logs alone.

Implementation Description (bullets):
Log the endpoint that fails validation

Testing (What was existing testing like? What have you done to improve it?):
N/A

Concerns (what feedback would you like?):
It's a bit weird to use a constant string as a safe arg, but it works.

Where should we start reviewing?:
Diff

Priority (whenever / two weeks / yesterday):
ASAP.

[changelog-app]

Generate changelog in changelog/@unreleased

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

Log the endpoint when lock watch cache validations fail.

Check the box to generate changelog(s)

• Generate changelog entry