release-25.2: workloadccl: mark tpccmultidb as bigInitialData

[yuzefovich]

Backport 1/1 commits from #160209 on behalf of @yuzefovich.

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We already skip tpcc in bigInitialData, and I think it was a mistake that tpccmultidb wasn't marked in the same way. In particular, this will make it so that we don't run some of the test cases.

The reason I was looking into this is that TestAllRegisteredSetup/tpccmultidb took 9 minutes on CI with external process mode. I couldn't quickly speed that up (e.g. exempting from rate limiting didn't help), but skipping it will work just fine.

Epic: None
Release note: None

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Release justification: test-only change.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that it falls into one of the following categories (select one):

• Non-production code changes. Includes test-only changes, build system changes, etc.
• Fixes for serious issues. Defined in the policy as correctness, stability, or security issues, data corruption/loss, significant performance regressions, breaking working and widely used functionality, or an inability to detect and debug production issues.
• Other approved changes. These changes must be gated behind a disabled-by-default feature flag unless there is a strong justification not to.

Add a brief release justification to the PR description explaining your selection.

Also, confirm that the change does not break backward compatibility and complies with all aspects of the backport policy.

All backports must be reviewed by the TL and EM for the owning area.

[blathers-crl]

✅ PR #160452 is compliant with backport policy

Confidence: high
Backward compatible: true
Explanation: The PR qualifies for an exemption under the 'Non-Production and Test-Only Changes' clause of the backport policy. The changed file, 'pkg/ccl/workloadccl/allccl/all_test.go', has an '_test.go' suffix, indicating that it is a test file. Test files are specified in the policy as non-production code, and changes affecting them do not require critical bug justifications or feature flag gating. Additionally, the PR body includes a 'Release justification: test-only change.' statement, which clearly labels this as a test-only modification, giving further support for its compliance.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is