build: fix flaky build

[david-allison]

dotnet publish wanted to build tests even though they were not necessary

This started occurring after moving to net8.0

• Fixes #207

[david-allison]

Giving this 5 reruns of CI to confirm. Tested 10 times locally

• ✅ https://github.com/david-allison/manx-corpus-search/actions/runs/9005366198/job/24740496157?pr=216
• ✅ https://github.com/david-allison/manx-corpus-search/actions/runs/9005391421
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