Update dependency ex_doc to ~> 0.29.0 (master)

[appcues-wss[bot]]

This PR contains the following updates:

Package	Update	Change
ex_doc	minor	~> 0.26.0 -> ~> 0.29.0

---

Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• [ ] If you want to rebase/retry this PR, click this checkbox.

[appcues-wss[bot]]

⚠ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

♻ Renovate will retry this branch, including artifacts, only when one of the following happens:

• any of the package files in this branch needs updating, or
• the branch becomes conflicted, or
• you click the rebase/retry checkbox if found above, or
• you rename this PR's title to start with "rebase!" to trigger it manually

The artifact failure details are included below:

File name: mix.lock

Command failed: mix deps.update ex_doc
/opt/buildpack/tools/erlang/24.3.4.1/bin/erl: 34: exec: /usr/local/erlang/24.3.4.1/erts-12.3.2.1/bin/erlexec: not found