test_runner: fix neon_local usage for version mismatch tests (#10859)

## Problem

Tests with mixed versions of binaries always pick up new versions if
services are started using `neon_local`.

## Summary of changes
- Set `neon_local_binpath` along with `neon_binpath` and
`pg_distrib_dir` for tests with mixed versions

test_runner/fixtures/neon_fixtures.py

@@ -491,6 +491,7 @@ def __init__(
         self.test_may_use_compatibility_snapshot_binaries = False
         self.version_combination = combination
         self.mixdir = self.test_output_dir / "mixdir_neon"
+
         if self.version_combination is not None:
             assert (
                 self.compatibility_neon_binpath is not None
@@ -702,6 +703,11 @@ def ignore_postgres_log(path: str, _names):
 
     def _mix_versions(self):
         assert self.version_combination is not None, "version combination must be set"
+
+        # Always use a newer version of `neon_local`
+        (self.mixdir / "neon_local").symlink_to(self.neon_binpath / "neon_local")
+        self.neon_local_binpath = self.mixdir
+
         for component, paths in COMPONENT_BINARIES.items():
             directory = (
                 self.neon_binpath
@@ -711,9 +717,10 @@ def _mix_versions(self):
             for filename in paths:
                 destination = self.mixdir / filename
                 destination.symlink_to(directory / filename)
+        self.neon_binpath = self.mixdir
+
         if self.version_combination["compute"] == "old":
             self.pg_distrib_dir = self.compatibility_pg_distrib_dir
-        self.neon_binpath = self.mixdir
 
     def overlay_mount(self, ident: str, srcdir: Path, dstdir: Path):
         """

test_runner/fixtures/utils.py

@@ -52,11 +52,11 @@
 # Disable auto-formatting for better readability
 # fmt: off
 VERSIONS_COMBINATIONS = (
-    {"storage_controller": "new", "storage_broker": "new", "compute": "new", "safekeeper": "new", "pageserver": "new"},
-    {"storage_controller": "new", "storage_broker": "new", "compute": "old", "safekeeper": "old", "pageserver": "old"},
-    {"storage_controller": "new", "storage_broker": "new", "compute": "old", "safekeeper": "old", "pageserver": "new"},
-    {"storage_controller": "new", "storage_broker": "new", "compute": "old", "safekeeper": "new", "pageserver": "new"},
-    {"storage_controller": "old", "storage_broker": "old", "compute": "new", "safekeeper": "new", "pageserver": "new"},
+    {"storage_controller": "new", "storage_broker": "new", "compute": "new", "safekeeper": "new", "pageserver": "new"}, # combination: nnnnn
+    {"storage_controller": "new", "storage_broker": "new", "compute": "old", "safekeeper": "old", "pageserver": "old"}, # combination: ooonn
+    {"storage_controller": "new", "storage_broker": "new", "compute": "old", "safekeeper": "old", "pageserver": "new"}, # combination: ononn
+    {"storage_controller": "new", "storage_broker": "new", "compute": "old", "safekeeper": "new", "pageserver": "new"}, # combination: onnnn
+    {"storage_controller": "old", "storage_broker": "old", "compute": "new", "safekeeper": "new", "pageserver": "new"}, # combination: nnnoo
 )
 # fmt: on