pubdev: Update User-Agent request header value

Use a value that matches good practice recommended by pub.dev REST API doc.

https://github.com/dart-lang/pub/blob/master/doc/repository-spec-v2.md

swh/lister/pubdev/lister.py

@@ -14,9 +14,15 @@ from swh.lister.utils import throttling_retry
 from swh.scheduler.interface import SchedulerInterface
 from swh.scheduler.model import ListedOrigin
 
-from .. import USER_AGENT
+from .. import __version__
 from ..pattern import CredentialsType, StatelessLister
 
+# https://github.com/dart-lang/pub/blob/master/doc/repository-spec-v2.md#metadata-headers
+USER_AGENT = (
+    f"Software Heritage PubDev Lister v{__version__} "
+    "(+https://www.softwareheritage.org/contact)"
+)
+
 logger = logging.getLogger(__name__)
 
 # Aliasing the page results returned by `get_pages` method from the lister.

swh/lister/pubdev/tests/test_lister.py

@@ -3,7 +3,7 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
-from swh.lister.pubdev.lister import PubDevLister
+from swh.lister.pubdev.lister import USER_AGENT, PubDevLister
 
 expected_origins = {
     "https://pub.dev/packages/Autolinker",
@@ -28,11 +28,19 @@ def test_pubdev_lister(datadir, requests_mock_datadir, swh_scheduler):
         assert origin.last_update is not None
 
 
+def _match_request(request):
+    return request.headers.get("User-Agent") == USER_AGENT
+
+
 def test_pubdev_lister_skip_package(
     datadir, requests_mock_datadir, swh_scheduler, requests_mock
 ):
 
-    requests_mock.get("https://pub.dev/api/packages/Autolinker", status_code=404)
+    requests_mock.get(
+        "https://pub.dev/api/packages/Autolinker",
+        status_code=404,
+        additional_matcher=_match_request,
+    )
 
     lister = PubDevLister(scheduler=swh_scheduler)
     res = lister.run()