fix(prevent): Allow members to update config

[suejung-sentry]

We got feedback that we want members to be allowed to update config for the PR Review in order to change the type and frequency of reviews. Since this is in beta, there are no billing implications (where a member can create much higher usage that would then get billed). This is aligned with like Seer project settings and Github Integrations settings which allows members to edit.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
41201	1	41200	250

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

tests.sentry.prevent.endpoints.test_pr_review_config.OrganizationPreventGitHubConfigTest::test_invalid_config_schema_returns_400

Stack Traces | 2.52s run time

#x1B[1m#x1B[.../prevent/endpoints/test_pr_review_config.py#x1B[0m:53: in test_invalid_config_schema_returns_400
    assert "'github_organizations' is a required property" in resp.data["detail"]
#x1B[1m#x1B[31mE   assert "'github_organizations' is a required property" in 'Invalid config'#x1B[0m

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[getsantry]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you add the label WIP, I will leave it alone unless WIP is removed ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀