Update Pub/Sub generated client retry configuration.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/PubSub/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:5fd9aee1d82a00cebf425c8fa431f5457539562f5867ad9c54370f0ec9a7ccaa
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/pubsub/artman_pubsub.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-pubsub-v1.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/Gapic/PublisherGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/Gapic/SubscriberGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/PublisherClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/PublisherGrpcClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/SubscriberClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/SubscriberGrpcClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/PublisherClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/SubscriberClientTest.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/System/V1/PublisherSmokeTest.php.
synthtool > No replacements made in src/**/*.php for pattern <a href="/pubsub/docs/, maybe replacement is not longer needed?
synthtool > Cleaned up 1 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@82f4726). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1675   +/-   ##
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  Coverage          ?   90.66%           
  Complexity        ?     4334           
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  Files             ?      302           
  Lines             ?    12775           
  Branches          ?        0           
=========================================
  Hits              ?    11582           
  Misses            ?     1193           
  Partials          ?        0

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