Bump gui from af585e6 to 615fde9

Bumps [gui](https://github.com/openevse/openevse_wifi_gui) from `af585e6` to `615fde9`.
- [Release notes](https://github.com/openevse/openevse_wifi_gui/releases)
- [Commits](OpenEVSE/openevse_wifi_gui@af585e6...615fde9)

---
updated-dependencies:
- dependency-name: gui
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>