feat: Add INTERNAL as a retryable error code

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/Kms/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
0.29.1: Pulling from googleapis/artman
Digest: sha256:b2a73f4dda03ef8fcaa973e3ba26d0cf34091f6c22c70add663af325931aef4d
Status: Image is up to date for googleapis/artman:0.29.1
synthtool > Cloning googleapis.
synthtool > Running generator for google/cloud/kms/artman_cloudkms.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/php/google-cloud-kms-v1.
synthtool > Replaced "'serviceAddress' =>" in src/V1/Gapic/KeyManagementServiceGapicClient.php.
synthtool > Replaced '@type string \\$serviceAddress\\n\\s+\\*\\s+The address' in src/V1/Gapic/KeyManagementServiceGapicClient.php.
synthtool > Replaced '\\$transportConfig, and any \\$serviceAddress' in src/V1/Gapic/KeyManagementServiceGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/KeyManagementServiceGrpcClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/KeyManagementServiceClient.php.
synthtool > Replaced 'Copyright \\d{4}' in src/V1/Gapic/KeyManagementServiceGapicClient.php.
synthtool > Replaced 'Copyright \\d{4}' in tests/Unit/V1/KeyManagementServiceClientTest.php.
synthtool > No replacements made in src/V1/Gapic/KeyManagementServiceGapicClient.php for pattern CryptoKey_CryptoKeyPurpose, maybe replacement is not longer needed?
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKeyVersion_CryptoKeyVersionAlgorithm.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKey_CryptoKeyPurpose.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKeyVersion_CryptoKeyVersionView.php.
synthtool > Replaced 'will be removed in the next major release' in src/V1/CryptoKeyVersion_CryptoKeyVersionState.php.
synthtool > Cleaned up 1 temporary directories.
synthtool > Wrote metadata to synth.metadata.

[codecov]

Codecov Report

Merging #2248 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master   #2248   +/-   ##
========================================
  Coverage      92.6%   92.6%           
  Complexity     4452    4452           
========================================
  Files           307     307           
  Lines         13273   13273           
========================================
  Hits          12292   12292           
  Misses          981     981

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