(chore) update tests in light-clients/06-solomachine to expect specific error

[PrathyushaLakkireddy]

Description

ref: #7175

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• Linked to GitHub issue with discussion and accepted design, OR link to spec that describes this work.
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• Wrote unit and integration tests.
• Updated relevant documentation (docs/).
• Added relevant godoc comments.
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• Include a descriptive changelog entry when appropriate. This may be left to the discretion of the PR reviewers. (e.g. chores should be omitted from changelog)
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[DimitrisJim]

hi, let me take care of merging main. The runners are getting swamped, thanks!