Restore legacy support of >> PyPI requirements

This was restored with the introduction of packvers

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

tests/packagedcode/data/pypi/requirements_txt/invalid_spec/output.expected.json

@@ -28,7 +28,29 @@
     "source_packages": [],
     "file_references": [],
     "extra_data": {},
-    "dependencies": [],
+    "dependencies": [
+      {
+        "purl": "pkg:pypi/test",
+        "extracted_requirement": "test>>1.2.0",
+        "scope": "install",
+        "is_runtime": true,
+        "is_optional": false,
+        "is_resolved": false,
+        "resolved_package": {},
+        "extra_data": {
+          "is_editable": false,
+          "link": null,
+          "hash_options": [],
+          "is_constraint": false,
+          "is_archive": null,
+          "is_wheel": false,
+          "is_url": null,
+          "is_vcs_url": null,
+          "is_name_at_url": false,
+          "is_local_path": null
+        }
+      }
+    ],
     "repository_homepage_url": null,
     "repository_download_url": null,
     "api_data_url": null,