Reword "no sourcemap ref"

[szokeasaurusrex]

In the sourcemaps upload command, we output "no sourcemap ref" for any JS source file for which we cannot find a sourcemap. We should reword this to something clearer, using full words and not abbreviations. For example, we could use "no source map reference" or "no source map found."

See here for more context. Thanks @lforst for the suggestion!

[github-actions[bot]]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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