pull requests do not build anymore

[LokiMidgard]

like in #705

Error: Unable to process command '::set-env name=DOTNET_ROOT::../share/dotnet' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/
Error: Unable to process command '::add-path::/opt/hostedtoolcache/GitVersion.Tool/5.2.4/x64' successfully.
Error: The `add-path` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

and here

Error: Unable to process command '::set-env name=DOTNET_CLI_TELEMETRY_OPTOUT::1' successfully.
Error: The `set-env` command is disabled. Please upgrade to using Environment Files or opt into unsecure command execution by setting the `ACTIONS_ALLOW_UNSECURE_COMMANDS` environment variable to `true`. For more information see: https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

[lithiumtoast]

Yup, it's a problem with GitVersion. I already have a fix for it, I'll push the change soon.