chore: fix trivy pipeline by pulling trivy image from mcr

[jwtty]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
The trivy action was failing from time to time due to throttling when pulling trivy image from ghcr.io registry. Thus we switch to use mcr instead.

Which issue(s) this PR fixes:

Fixes #

Requirements:

• run make reviewable for basic local test
• Read and followed fleet-networking's Code of conduct.
• uses conventional commit messages
• includes documentation
• adds unit tests

How has this code been tested

Tested in the fleet repo PR: Azure/fleet#948

Special notes for your reviewer

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.69%. Comparing base (0cb38e4) to head (a5562b0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #213      +/-   ##
==========================================
+ Coverage   78.48%   78.69%   +0.21%     
==========================================
  Files          27       27              
  Lines        3699     3699              
==========================================
+ Hits         2903     2911       +8     
+ Misses        641      634       -7     
+ Partials      155      154       -1     

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