fixed "dotnet publish" line

[AgentBelfort]

While studying Docker Language-specific guides I came across a problem:

=> ERROR [server build 4/5] RUN --mount=type=cache,id=nuget,target=/root/.nuget/packages     dotnet publish -a ${TARGETARCH/amd64/x64} --use-current-runtime --self-contained false -o /app                                  0.5s 

> [server build 4/5] RUN --mount=type=cache,id=nuget,target=/root/.nuget/packages     dotnet publish -a ${TARGETARCH/amd64/x64} --use-current-runtime --self-contained false -o /app:
0.455 MSBuild version 17.3.2+561848881 for .NET
0.456 MSBUILD : error MSB1011: Specify which project or solution file to use because this folder contains more than one project or solution file.

failed to solve: process "/bin/sh -c dotnet publish -a ${TARGETARCH/amd64/x64} --use-current-runtime --self-contained false -o /app" did not complete successfully: exit code: 1

This problem was fixed by me and updated in my fork