doc: require two approvals to land changes

Currently, changes require approval by one Collaborator in most cases.
However there are situations where two approvals are required. For
example, breaking changes require two approvals from TSC members. And
fast-tracking a request requires two approvals.

Additionally, although only one approval is strictly required, in
practice, we nearly always seek a second approval when there is only
one.

Lastly, concerns have been raised about (perhaps unintentionally) gaming
the one-approval system by suggesting a change to someone else, and then
approving that change when the user submits a pull request. This
resolves (or at least mitigates) that concern.

Fixes: https://github.com/nodejs/node/issues/19564

PR-URL: https://github.com/nodejs/node/pull/22255
Refs: https://github.com/nodejs/node/issues/19564
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Bryan English <bryan@bryanenglish.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: John-David Dalton <john.david.dalton@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: George Adams <george.adams@uk.ibm.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

COLLABORATOR_GUIDE.md

@@ -112,10 +112,11 @@ comment that explains why the PR does not require a CI run.
 
 ### Code Reviews
 
-All pull requests must be reviewed and accepted by a Collaborator with
+At least two Collaborators must approve a pull request before the pull request
-sufficient expertise who is able to take full responsibility for the
+lands. (One Collaborator approval is enough if the pull request has been open
-change. In the case of pull requests proposed by an existing
+for more than 7 days.) Approving a pull request indicates that the Collaborator
-Collaborator, an additional Collaborator is required for sign-off.
+accepts responsibility for the change. Approval must be from Collaborators who
+are not authors of the change.
 
 In some cases, it may be necessary to summon a GitHub team to a pull request for
 review by @-mention.

GOVERNANCE.md

@@ -32,11 +32,13 @@ Their privileges include but are not limited to:
 Modifications of the contents of the nodejs/node repository are made on
 a collaborative basis. Anybody with a GitHub account may propose a
 modification via pull request and it will be considered by the project
-Collaborators. All pull requests must be reviewed and accepted by a
+Collaborators.
-Collaborator with sufficient expertise who is able to take full
+
-responsibility for the change. In the case of pull requests proposed
+At least two Collaborators must approve a pull request before the pull request
-by an existing Collaborator, an additional Collaborator is required
+lands. (One Collaborator approval is enough if the pull request has been open
-for sign-off.
+for more than 7 days.) Approving a pull request indicates that the Collaborator
+accepts responsibility for the change. Approval must be from Collaborators who
+are not authors of the change.
 
 If one or more Collaborators oppose a proposed change, then the change cannot
 be accepted unless: