Fix builds relation on Ci::RunnerManager

What does this MR do and why?

This MR fixes the Ci::RunnerManager#builds Active Record relation, which started failing after the rename of RunnerMachine to RunnerManager:

[49] pry(main)> ::Ci::RunnerManager.find(130).builds.to_a
  Ci::RunnerManager Load (4.5ms)  SELECT "ci_runner_machines".* FROM "ci_runner_machines" WHERE "ci_runner_machines"."id" = 130 LIMIT 1 /*application:console,db_config_name:ci,console_hostname:Pedros-MacBook-Pro-M1-Max.local,console_username:pedropombeiro,line:(pry):49:in `__pry__'*/
  Ci::Build Load (0.5ms)  SELECT "ci_builds".* FROM "ci_builds" INNER JOIN "p_ci_runner_machine_builds" ON "ci_builds"."id" = "p_ci_runner_machine_builds"."build_id" WHERE "ci_builds"."type" = 'Ci::Build' AND "p_ci_runner_machine_builds"."runner_manager_id" = 130 /*application:console,db_config_name:ci,console_hostname:Pedros-MacBook-Pro-M1-Max.local,console_username:pedropombeiro,line:(pry):49:in `__pry__'*/
ActiveRecord::StatementInvalid: PG::UndefinedColumn: ERROR:  column p_ci_runner_machine_builds.runner_manager_id does not exist
LINE 1: ...ld_id" WHERE "ci_builds"."type" = 'Ci::Build' AND "p_ci_runn...

I don't think this relation method is currently being used (but will be in an upcoming MR, hence this preliminary fix).

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

In the GDK console, run the following expression:

::Ci::RunnerManager.last.builds.to_a

It should return a collection, instead of the previous error.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Part of #415453 (closed)