build(deps): bump submodules/rest-api-specs from 18f9e9b to 03a6598 (#4770)

Bumps [submodules/rest-api-specs](https://github.com/Azure/azure-rest-api-specs) from `18f9e9b` to `03a6598`.
- [Release notes](https://github.com/Azure/azure-rest-api-specs/releases)
- [Commits](Azure/azure-rest-api-specs@18f9e9b...03a6598)

---
updated-dependencies:
- dependency-name: submodules/rest-api-specs
  dependency-version: 03a6598cdc38924f9eaaeb03f8ef151f5aeff449
  dependency-type: direct:production
...

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