20137: Fix incorrect keyword in RailsAPI config reload loop

20137: Fix incorrect keyword in RailsAPI config reload loop

The reason rails_restart_test.go has been racey is because the code
under test is actually buggy. If the configuration reload loop ever
encounters a condition where it wants to restart (probably
`hash == hash_lastload`), it tries to call a nonexistent method
`continue`, the thread crashes, the configuration never gets reloaded,
and the test fails.

Use the intended Ruby keyword `next` instead.
Closes #20137.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>