fix(workflows): Prevent shell injection in fast-revert workflow

[fix-it-felix-sentry]

Summary

This PR fixes a security finding by preventing potential shell injection in the fast-revert GitHub Actions workflow.

Changes

• Modified .github/workflows/fast-revert.yml to use environment variables instead of direct GitHub context interpolation in run: steps
• All GitHub context variables are now passed through the env: section and referenced as environment variables in the shell script
• Added proper quoting around environment variables to prevent injection

Security Details

The original code used direct interpolation of GitHub context variables (${{ ... }}) in shell commands, which could potentially allow code injection attacks. While the specific variables used (repository ID, run ID, etc.) are likely safe, following security best practices requires using intermediate environment variables.

Before:

run: |
  curl ... -H 'Authorization: token ${{ steps.token.outputs.token }}' ...

After:

env:
  GH_TOKEN: ${{ steps.token.outputs.token }}
run: |
  curl ... -H "Authorization: token $GH_TOKEN" ...

References

• Parent ticket: https://linear.app/getsentry/issue/VULN-1096
• Child ticket: https://linear.app/getsentry/issue/STREAM-694
• GitHub Actions Security Hardening
• Semgrep Rule

Testing

• YAML syntax validated
• No functional changes to the workflow behavior
• All GitHub context variables properly passed through environment variables

[linear]

VULN-1096 Command Injection vulnerability in getsentry/taskbroker .github/workflows/fast-revert.yml

[sentry]

Bug: When triggered via workflow_dispatch, the GH_REPO_ID variable is empty, causing the failure notification step to silently fail due to a malformed API URL.
_{Severity: MEDIUM}

Suggested Fix

Ensure the repository ID is correctly sourced for all trigger types. Instead of relying on github.event.repository.id, which is not present in workflow_dispatch events, use the universally available github.repository_id context variable to populate GH_REPO_ID.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: .github/workflows/fast-revert.yml#L49-L54

Potential issue: When the workflow is triggered via `workflow_dispatch`, the
`github.event.repository.id` context variable is unavailable. This results in the
`GH_REPO_ID` environment variable being set to an empty string. Consequently, the
'comment on failure' step constructs a malformed API URL
(`https://api.github.com/repositories//issues/...`) for its `curl` command. This causes
the API call to fail, silently preventing a failure notification comment from being
posted to the pull request if the main revert action fails. This issue only occurs with
the `workflow_dispatch` trigger.

_{Did we get this right? 👍 / 👎 to inform future reviews.}