Update "fetching_messages" example (#115)

This updates the "fetching_messages" example to remove a deprecated
method call in favor of the streaming `iter_messages`. Instead of
printing the length, it prints the timestamp, channel, and topic of each
message; for example:

```txt
1616425609698483083 | /gps/navheading          | sensor_msgs/Imu
1616425609700292327 | /gps/fix_velocity        | geometry_msgs/TwistWithCovarianceStamped
```

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ on:
 
 jobs:
   python:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     permissions:
       id-token: write
     steps:
@@ -23,6 +23,7 @@ jobs:
       - run: pipenv run black --check --diff --color --exclude '.*_pb2.py' .
       - run: pipenv run pyright foxglove
       - run: pipenv run python -m flake8 foxglove
+      - run: pipenv run python -m flake8 examples
       - run: pipenv run python -m pytest
       - run: pipenv run python -m build
 

examples/downloading_data.py

@@ -1,4 +1,3 @@
-import datetime
 from datetime import datetime, timedelta
 
 from foxglove.client import Client

examples/fetching_messages.py

@@ -1,4 +1,3 @@
-import datetime
 from datetime import datetime, timedelta
 
 from foxglove.client import Client
@@ -9,10 +8,9 @@
 
 # Make sure you've imported either the mcap-ros1-support or mcap-protobuf-support
 # libraries before making this call in order to get decoded messages.
-messages = client.get_messages(
+for schema, channel, message, decoded_message in client.iter_messages(
     device_id=device_id,
     start=datetime.now() - timedelta(hours=3),
     end=datetime.now() - timedelta(hours=1),
-)
-
-print(f"downloaded {len(messages)} messages")
+):
+    print(f"{message.log_time} | {channel.topic:<24} | {schema.name}")