Linux Docker build fails due to .NET 6

[nmcglo]

The Dockerfile in the current master branch uses a .NET SDK 5.0 base image which can't target .NET 6 targets.

Relevant output for docker build -t pgstosrt .

Step 4/9 : RUN cd /src &&     dotnet restore  &&     dotnet publish -c Release -o /src/PgsToSrt/out &&     mv /src/entrypoint.sh /entrypoint.sh && chmod +x /entrypoint.sh &&     mv /src/PgsToSrt/out /app
 ---> Running in 94e0c48afbe5
  Determining projects to restore...
/usr/share/dotnet/sdk/5.0.101/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.TargetFrameworkInference.targets(141,5): error NETSDK1045: The current .NET SDK does not support targeting .NET Core 6.0.  Either target .NET Core 5.0 or lower, or use a version of the .NET SDK that supports .NET Core 6.0. [/src/PgsToSrt/PgsToSrt.csproj]
The command '/bin/sh -c cd /src &&     dotnet restore  &&     dotnet publish -c Release -o /src/PgsToSrt/out &&     mv /src/entrypoint.sh /entrypoint.sh && chmod +x /entrypoint.sh &&     mv /src/PgsToSrt/out /app' returned a non-zero code: 1

Steps to reproduce:

git clone https://github.com/Tentacule/PgsToSrt.git
cd PgsToSrt

# checkout the latest release v1.4.2 or master at 38fd03e57f
git checkout v1.4.2

docker build -t pgstosrt .

Quick fix:

Change the .NET SDK base image to 6.0
Specify the framework to target net6.0 (because the project specifies both 5.0 or 6.0 as potential targets, one must be explicitly chosen)

Alternatively, leave the .NET SDK base image to 5.0.101
Specify the framework to target net5.0

[nmcglo]

This is also addressed in #28, hadn't seen that before I submitted #30 🤦‍♂️