fix: retry curl dotnet-install.sh

[jpnurmi]

After merging #2118, the first job in the main branch failed like this:

• Installing Linux Dependencies

  curl: (35) OpenSSL SSL_connect: Connection reset by peer in connection to dot.net:443 
  

• Build

  /__w/_temp/997abeb5-d2d0-41eb-ad62-073478c13323.sh: 2: dotnet: not found
  

This tweak makes it more robust by a) allowing curl to retry a few times should there be any network hiccups, and b) ensuring the dependency installation step fails as appropriate instead of quietly ignoring the error and proceeding to the build step.

#skip-changelog

[bitsandfoxes]

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