mobile: Load envoy_repo in the WORKSPACE

[fredyw]

This is to fix this error.

ERROR: Skipping '@envoy//tools/code_format:check_format': error loading package '@envoy//tools/code_format': Unable to find package for @envoy_repo//:path.bzl: The repository '@envoy_repo' could not be resolved: Repository '@envoy_repo' is not defined.

Risk Level: low
Testing: tools/check_format.sh fix
Docs Changes: n/a
Release Notes: n/a
Platform Specific Features: n/a

[repokitteh-read-only]

As a reminder, PRs marked as draft will not be automatically assigned reviewers,
or be handled by maintainer-oncall triage.

Please mark your PR as ready when you want it to be reviewed!

🐱

Caused by: #35758 was opened by fredyw.

see: more, trace.

[fredyw]

/assign @phlax