Builds of the esp32s2 targets frequently fail:
```
-- Found Git: /usr/bin/git (found version "2.28.0")
-- Initialising new submodule components/asio/asio...
warning: could not look up configuration 'remote.origin.url'. Assuming this repository is its own authoritative upstream.
Submodule 'components/asio/asio' (/home/runner/work/circuitpython/circuitpython/ports/espressif/asio.git) registered for path 'components/asio/asio'
fatal: repository '/home/runner/work/circuitpython/circuitpython/ports/espressif/asio.git' does not exist
fatal: clone of '/home/runner/work/circuitpython/circuitpython/ports/espressif/asio.git' into submodule path '/home/runner/work/circuitpython/circuitpython/ports/esp32s2/esp-idf/components/asio/asio' failed
Failed to clone 'components/asio/asio'. Retry scheduled
fatal: repository '/home/runner/work/circuitpython/circuitpython/ports/espressif/asio.git' does not exist
fatal: clone of '/home/runner/work/circuitpython/circuitpython/ports/espressif/asio.git' into submodule path '/home/runner/work/circuitpython/circuitpython/ports/esp32s2/esp-idf/components/asio/asio' failed
Failed to clone 'components/asio/asio' a second time, aborting
CMake Error at esp-idf/tools/cmake/git_submodules.cmake:48 (message):
Git submodule init failed for components/asio/asio
Call Stack (most recent call first):
esp-idf/tools/cmake/build.cmake:78 (git_submodule_check)
esp-idf/tools/cmake/build.cmake:160 (__build_get_idf_git_revision)
esp-idf/tools/cmake/idf.cmake:49 (__build_init)
esp-idf/tools/cmake/project.cmake:7 (include)
CMakeLists.txt:8 (include)
```
It's not clear how/why this happens--is it something to do with our
multithreaded build?. Attempt to clear it up by manually checking out these
submodules ourselves.
Since e121e267adacf6, the shared bindings matrix uses the stubs.
Therefore, we must build them! This should fix the failure to build
the docs on readthedocs.org.
Neither @sommersoft nor I saw this locally since we had previously built
the stubs. github CI didn't see it, because it manually builds the stubs
in an earlier step of the build process, and does not clean the tree
in between.
.. this makes it take a fraction of the time, at least on systems
with a lot of CPU threads. Even on my old laptop with a 2-core CPU
it reduces the time from 55s to 27s.
