update Rust to v1.91.1

[tzemanovic]

Describe your changes

Checklist before merging

• If this PR has some consensus breaking changes, I added the corresponding breaking:: labels
  • This will require 2 reviewers to approve the changes
• If this PR requires changes to the docs or specs, a corresponding PR is opened in the namada-docs repo
  • Relevant PR if applies:
• If this PR affects services such as namada-indexer or namada-masp-indexer, a corresponding PR is opened in that repo
  • Relevant PR if applies:

[mergify]

🧪 CI Insights

Here's what we observed from your CI run for 292882d.

🟢 All jobs passed!

But CI Insights is watching 👀