ci: pin Pipelock action to v3.4.0

[luckyPipewrench]

What changed

Pins the CI and fuzz security scans to the reviewed Pipelock v3.4.0 action commit.

[coderabbitai]

Important

• 🔍 Trigger review

This repository does not receive automatic reviews because it has fewer than 10 stars.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 214fc8ee-3a37-45eb-8fed-e16738460207

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