[FEATURE] Ignore dummy secret placeholders

[drqc]

Currently, gitguardian is blocking cicd for secret pa***xx . This is a placeholder that should be ignore

[drqc]

To add a dummy secret use ggshield secret ignore --name dummy-secret1 d670f070d6e1a1912a21bd62ab04d2cb490d62d34af75e858193abf497ba25da

The secret is in SHA (pa***xx)