SQLStore: Fix race condition in RecursiveQueriesAreSupported

[grobinson-grafana]

What is this feature?

This commit fixes a race condition in RecursiveQueriesAreSupported:

WARNING: DATA RACE
Read at 0x00c0022aa520 by goroutine 15652:
  github.com/grafana/grafana/pkg/services/sqlstore.(*SQLStore).RecursiveQueriesAreSupported()
      /Users/grobinson/go/src/github.com/grafana/grafana/pkg/services/sqlstore/sqlstore.go:527 +0x34
  github.com/grafana/grafana/pkg/services/dashboards/database.(*dashboardStore).FindDashboards()
      /Users/grobinson/go/src/github.com/grafana/grafana/pkg/services/dashboards/database/database.go:963 +0x54

Previous write at 0x00c0022aa520 by goroutine 15648:
  github.com/grafana/grafana/pkg/services/sqlstore.(*SQLStore).RecursiveQueriesAreSupported()
      /Users/grobinson/go/src/github.com/grafana/grafana/pkg/services/sqlstore/sqlstore.go:559 +0xa0
  github.com/grafana/grafana/pkg/services/dashboards/database.(*dashboardStore).FindDashboards()
      /Users/grobinson/go/src/github.com/grafana/grafana/pkg/services/dashboards/database/database.go:963 +0x54

Why do we need this feature?

[Add a description of the problem the feature is trying to solve.]

Who is this feature for?

[Add information on what kind of user the feature is for.]

Which issue(s) does this PR fix?:

Fixes #

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[grafana-delivery-bot]

Hello @grobinson-grafana!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If the pull request modifies CI behaviour, please add the type/ci label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!

[grafana-delivery-bot]

Hello @grobinson-grafana!
Backport pull requests need to be either:

• Pull requests which address bugs,
• Urgent fixes which need product approval, in order to get merged,
• Docs changes.

Please, if the current pull request addresses a bug fix, label it with the type/bug label.
If it already has the product approval, please add the product-approved label. For docs changes, please add the type/docs label.
If the pull request modifies CI behaviour, please add the type/ci label.
If none of the above applies, please consider removing the backport label and target the next major/minor release.
Thanks!