chore: bump step-security/harden-runner to v2.19.0 (#198)

## Summary
- Bump `step-security/harden-runner` to `v2.19.0` (SHA
`8d3c67de8e2fe68ef647c8db1e6a09f647780f40`), the latest release
(2026-04-20).
- Replaces older pins so all workflows in this repo meet the ≥v2.17.0
org hardening bar.

Automated bump as part of an org-wide audit; no config flags changed.

## Test plan
- [ ] CI passes on this PR
- [ ] harden-runner initializes with the existing `egress-policy` in
each workflow

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: antitree

.github/workflows/actionlint.yaml

@@ -24,7 +24,7 @@ jobs:
     name: Action lint
     runs-on: ubuntu-latest
     steps:
-      - uses: step-security/harden-runner@fe104658747b27e96e4f7e80cd0a94068e53901d # v2.16.1
+      - uses: step-security/harden-runner@8d3c67de8e2fe68ef647c8db1e6a09f647780f40 # v2.19.0
         with:
           egress-policy: block
           allowed-endpoints: >

.github/workflows/ghaudit.yaml

@@ -18,7 +18,7 @@ jobs:
 
     steps:
     - name: Harden the runner (Audit all outbound calls)
-      uses: step-security/harden-runner@fe104658747b27e96e4f7e80cd0a94068e53901d # v2.16.1
+      uses: step-security/harden-runner@8d3c67de8e2fe68ef647c8db1e6a09f647780f40 # v2.19.0
       with:
         egress-policy: audit
 

.github/workflows/zizmor.yaml

@@ -26,7 +26,7 @@ jobs:
       contents: read # Clone the repository
       security-events: write # Upload SARIF results to Code Scanning
     steps:
-      - uses: step-security/harden-runner@fe104658747b27e96e4f7e80cd0a94068e53901d # v2.16.1
+      - uses: step-security/harden-runner@8d3c67de8e2fe68ef647c8db1e6a09f647780f40 # v2.19.0
         with:
           egress-policy: block
           allowed-endpoints: >