poetry: Export dependencies in new constraints format

The format 'requirements.txt' is no longer compatible with pip contraints.
This change adapts the poetry export call to use the new
'constraints.txt' format.

see also: python-poetry/poetry-plugin-export#125

noxfile.py

@@ -20,7 +20,7 @@ def install_with_constraints(session: Session, *args: str, **kwargs: Any) -> Non
             "poetry",
             "export",
             "--with", "dev",
-            "--format=requirements.txt",
+            "--format=constraints.txt",
             "--without-hashes",
             f"--output={requirements.name}",
             external=True,
@@ -78,7 +78,7 @@ def safety(session: Session) -> None:
             "poetry",
             "export",
             "--with", "dev",
-            "--format=requirements.txt",
+            "--format=constraints.txt",
             "--without-hashes",
             f"--output={requirements.name}",
             external=True,