Tell pip-compile not to include backports.asyncio.runner

The package backports.asyncio.runner is a transitive dependency that
should only be installed for Python < 3.11. It doesn't need to be in the
requirements files we produce, and conversely, letting `pip-compile`
include it leads to installation failures with some Python versions. We
can tell `pip-compile` to omit it and this solves the problem.

Author: mhucka

dev_tools/requirements/run-pip-compiles.py

@@ -100,6 +100,10 @@ def pip_compile(env_name: str, env_recipe: EnvRecipe, env_out_dir: str, constrai
             "pip-compile",
             f"--output-file={env_out_dir}/{env_name}.env.txt",
             "--resolver=backtracking",
+            # The following is a transitive dependency that should only be
+            # installed for Python < 3.11. It doesn't need to be in the
+            # requirements files we produce, so tell pip-compile to omit it.
+            "--unsafe-package", "backports.asyncio.runner",
         ]
         + dep_args
     )