Fix code scanning alert - Token-Permissions: .github/workflows/pr-title.yml

[ianlewis]

.github/workflows/pr-title.yml:1:
score is 0: no topLevel permission defined
Remediation tip: Visit https://app.stepsecurity.io/secureworkflow.
Tick the 'Restrict permissions for GITHUB_TOKEN'
Untick other options
NOTE: If you want to resolve multiple issues at once, you can visit https://app.stepsecurity.io/securerepo instead.
Click Remediation section below for further remediation help

Tracking issue for:

• https://github.com/slsa-framework/slsa-verifier/security/code-scanning/9