fix(oauth): add locking to prevent race conditions in grant exchange

[mdtro]

Pulled from #82052 to break out these changes into smaller PRs.

Use locks to ensure an ApiGrant cannot be used twice during a race condition that would result in multiple access/refresh token pairs.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
23595	1	23594	290

View the top 1 failed test(s) by shortest run time

tests.sentry.sentry_apps.token_exchange.test_grant_exchanger.TestGrantExchanger::test_race_condition_on_grant_exchange

Stack Traces | 2.66s run time

#x1B[1m#x1B[.../sentry_apps/token_exchange/test_grant_exchanger.py#x1B[0m:120: in test_race_condition_on_grant_exchange
    with pytest.raises(UnableToAcquireLock):
#x1B[1m#x1B[31mE   Failed: DID NOT RAISE <class 'sentry.utils.locking.UnableToAcquireLock'>#x1B[0m

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