### Discussion
Upgrade `lerna` from `4.x` to `9.x`. This newer version of `lerna` is powered by `NX`, which also requires a newer minor version bump of `node` in our workflows, and slight changes our test execution parms.
The new version of Lerna is said to improve performance, and that seems to have exacerbated race conditions in the Auth test suites (@firebase/auth and @firebase/auth-compat). To resolve intermittent CI failures caused by these race conditions, I've configured these tests to run in serial instead of concurrently.
Also I needed to bump the node version of our workflows by 2 minor versions (20.10.0 -> 2.12.0) because Lerna 9.0.6 isn't supported in Node 20.10.0.
### Testing
- Clean repo, clean cache, clean dependency installs.
- CI, local builds and tests.
Note: The Firestore WebKit failure in the optional CI execution list is a known issue (b/524995481).
### API Changes
None.
