Bump leptos from 0.6.15 to 0.7.7 in /pixie-web

Bumps [leptos](https://github.com/leptos-rs/leptos) from 0.6.15 to 0.7.7.
- [Release notes](https://github.com/leptos-rs/leptos/releases)
- [Commits](leptos-rs/leptos@v0.6.15...v0.7.7)

---
updated-dependencies:
- dependency-name: leptos
  dependency-version: 0.7.7
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]