python: Run make install with -j1

Python's install target is not parallel-safe.  We used to do this, but
then `-j1` got lost in one of the refactors and that miraculously
worked, but success is not guaranteed, so revert back to running with
`-j1`.

edgedbpkg/python/__init__.py

@@ -1,4 +1,7 @@
 from __future__ import annotations
+from typing import (
+    Mapping,
+)
 
 import pathlib
 import platform
@@ -246,6 +249,14 @@ def get_make_install_env(self, build: targets.Build, wd: str) -> str:
         env = super().get_make_install_env(build, wd)
         return f"{env} ENSUREPIP=no"
 
+    def get_make_install_args(
+        self,
+        build: targets.Build,
+    ) -> Mapping[str, str | pathlib.Path | None]:
+        args = dict(super().get_make_args(build))
+        args["-j"] = "1"
+        return args
+
     def get_build_install_script(self, build: targets.Build) -> str:
         script = super().get_build_install_script(build)
         installdest = build.get_install_dir(self, relative_to="pkgbuild")