[Feature Request]: Write integration tests for DICOM IO (Java SDK)

### What would you like to happen?

Currently, we don't have sufficient coverage for DICOM IO (Java SDK), as [DicomIOReadIT](https://github.com/apache/beam/blob/feb1cf73a09670d44edb633c8851a780024b2230/sdks/java/io/google-cloud-platform/src/test/java/org/apache/beam/sdk/io/gcp/healthcare/DicomIOReadIT.java#L36) is a no-op.

We should author integration tests for this IO to ensure functionality works correctly.

### Issue Priority

Priority: 2 (default / most feature requests should be filed as P2)

### Issue Components

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- [X] Component: Java SDK
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