pageserver: add no_sync for use in regression tests (2/2) (#9678)

## Problem

Followup to #9677 which enables
`no_sync` in tests. This can be merged once the next release has
happened.

## Summary of changes

- Always run pageserver with `no_sync = true` in tests.

test_runner/fixtures/neon_fixtures.py

@@ -1065,6 +1065,9 @@ def __init__(self, config: NeonEnvBuilder):
                 "http_auth_type": http_auth_type,
                 # Default which can be overriden with `NeonEnvBuilder.pageserver_config_override`
                 "availability_zone": "us-east-2a",
+                # Disable pageserver disk syncs in tests: when running tests concurrently, this avoids
+                # the pageserver taking a long time to start up due to syncfs flushing other tests' data
+                "no_sync": True,
             }
             if self.pageserver_virtual_file_io_engine is not None:
                 ps_cfg["virtual_file_io_engine"] = self.pageserver_virtual_file_io_engine