ci: run the fetch package's test suite

[pyramation]

Summary

packages/fetch has 21 tests that have never run in CI — the test job's matrix is a hand-maintained list and fetch was simply never added to it. That is how #119 (the *.localhost loopback pin, shipped in @constructive-io/fetch@1.2.0 and now consumed by constructive-db#2846) merged green without its regression tests ever executing on a runner. Those tests bind real IPv4/IPv6/DNS listeners, so they're exactly the kind that shouldn't be trusted to a local run only.

         package:
           - confstash
+          - fetch
           - fetch-api-client

Worth noting the same gap exists for nine other packages that declare a test script but aren't in the matrix — cel-proto-parser, graphile-pnpm-policy, inquirerer-test, kubernetes-test, rego-deparser, schema-ts-cli, toml-ast, visual-diff, yamlize-cli (three of them have no test files at all). Left alone here to keep this PR to the one package under discussion; deriving the matrix from the workspace instead of hand-maintaining it would kill the whole class of drift.

Link to Devin session: https://app.devin.ai/sessions/6f4d8dd9a5834871a379b7e598ccde8c
Requested by: @pyramation

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