release-23.1: sql: use high priority for populating RoleMemberCache

[blathers-crl]

Backport 1/1 commits from #117258 on behalf of @Xiang-Gu.

/cc @cockroachdb/release

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Previously, when the RoleMemberCache is invalid, it launches a new txn in a singleflight to read from system.role_members table to populate the cache. If, however, the original txn has previously laid a write intent on the same system table, then we end up having a deadlock: original txn waits for this new txn; this new txn waits for original txn.

Fixes #117144
Release note (bug fix): Fixed a bug where concurrent GRANTs can cause deadlocks.

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Release justification: important bug fixes

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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  issues or test-only changes.
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[cockroach-teamcity]

This change is