Fix firstInterimResponseStart name on diagram

[tunetheweb]

firstInterimResponseStart went through some bikeshedding on the name in w3c/resource-timing#345. Looks like the diagram was updated with interimResponseStart without the first which is what landed.

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Preview | Diff

[tunetheweb]

Anyone any idea why CI is failing?

[yoavweiss]

Seems like respec errors:

[FATAL] Error: Errors found during processing.
          at run (file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.0.2_typescript@5.4.4/node_modules/respec/tools/respec2html.js:258:11)
          at async file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.0.2_typescript@5.4.4/node_modules/respec/tools/respec2html.js:205:5
    Command `respec -s "http://localhost:3000/index.html?gitRevision=5c1fde5731b5125ff543556f502f5d14c59a3dc0" -o "index.html.built.html" --verbose -t 20 -e` failed with exit code: 1.
    ```

Might be unrelated to your change..

[tunetheweb]

This seemed to break the build. Not sure why, and can't find any associated change in https://github.com/speced/respec/ but this line isn't in Resource Timing and doesn't seem to be needed.