test: install the busy handler the test assumes

The unrestorable busy wait test assumed that its connection already had
a Ruby busy handler, which PRAGMA busy_timeout reads as 0. Rails 7.2
and later install that handler on each new connection, and an earlier
sync call installs it too. A new Rails 7.1 connection instead uses
SQLite's own busy_timeout, which PRAGMA reads as 5000.

When the test ran first on Rails 7.1, the adapter correctly took the
restorable path and put back SQLite's own wait. That wait holds the
Ruby VM lock, so the releaser thread could not release the write lock,
and the write raised SQLite3::BusyException after 5 s. Seed 11785
failed every time; CI run 35874660739 failed the same way.

Install the handler in the test and assert that PRAGMA reads 0, so the
test checks the unrestorable path on every Rails version and order.

Author: cardmagic

test/integration/synchronous_invocation_test.rb

@@ -588,7 +588,10 @@ def wait(timeout:)
     database_adapter = SolidObjects.database_adapter
     database_adapter.define_singleton_method(:configured_busy_handler_timeout) { |_connection| nil }
 
-    SolidObjects::Record.connection_pool.with_connection do
+    SolidObjects::Record.connection_pool.with_connection do |connection|
+      connection.raw_connection.busy_handler_timeout = configured_sqlite_busy_handler_timeout
+      assert_equal 0, connection.select_value("PRAGMA busy_timeout").to_i
+
       CounterActor.ref("unrestorable").increment
 
       assert_nothing_raised do