test: fix test_neon_cli_basics flakyness without making it better for future (#4827)

The test was starting two endpoints on the same branch as discovered by
@petuhovskiy.

The fix is to allow passing branch-name from the python side over to
neon_local, which already accepted it.

Split from #4824, which will handle making this more misuse resistant.

test_runner/fixtures/neon_fixtures.py

@@ -1504,6 +1504,7 @@ class NeonCli(AbstractNeonCli):
         safekeepers: Optional[List[int]] = None,
         tenant_id: Optional[TenantId] = None,
         lsn: Optional[Lsn] = None,
+        branch_name: Optional[str] = None,
     ) -> "subprocess.CompletedProcess[str]":
         args = [
             "endpoint",
@@ -1517,8 +1518,11 @@ class NeonCli(AbstractNeonCli):
             args.append(f"--lsn={lsn}")
         args.extend(["--pg-port", str(pg_port)])
         args.extend(["--http-port", str(http_port)])
+
         if safekeepers is not None:
             args.extend(["--safekeepers", (",".join(map(str, safekeepers)))])
+        if branch_name is not None:
+            args.extend(["--branch-name", branch_name])
         if endpoint_id is not None:
             args.append(endpoint_id)
 

test_runner/regress/test_neon_local_cli.py

@@ -16,11 +16,13 @@ def test_neon_cli_basics(neon_env_builder: NeonEnvBuilder, port_distributor: Por
             endpoint_id="ep-basic-main", pg_port=pg_port, http_port=http_port
         )
 
-        env.neon_cli.create_branch(new_branch_name="migration_check")
+        branch_name = "migration-check"
+
+        env.neon_cli.create_branch(new_branch_name=branch_name)
         pg_port = port_distributor.get_port()
         http_port = port_distributor.get_port()
         env.neon_cli.endpoint_start(
-            endpoint_id="ep-migration_check", pg_port=pg_port, http_port=http_port
+            f"ep-{branch_name}", pg_port, http_port, branch_name=branch_name
         )
     finally:
         env.neon_cli.stop()