LambdaNETCoreDeploy task attempts to build for .NET core 1.0.0 instead of 3.1 when using custom feeds

**Describe the bug**

When building a deployment package for a .NET core 3.1 project with the LambdaNETCoreDeploy task after restoring packages from custom feeds, the task fails because it attempts to build for .NET core 1.0 which is no longer available

**To reproduce**

1. Create a project targeting .NET core 3.1 referencing packages from custom feeds
2. Create a pipeline with following tasks:
- nuget restore from custom feed
- LambdaNETCoreDeploy, Create deployment package only
3. Run the Pipeline
4. The pipeline fails with `The framework 'Microsoft.NETCore.App', version '1.0.0' was not found.`

**Expected behavior**

The pipeline succeeds and builds a deployment package targeting netcoreapp3.1 as specified in the .csproj

**Your Environment**

- On-prem or cloud based?: cloud
- AWS Toolkit for Azure DevOps version: 1.7.0

**Additional context**

Packaging the project manually with `dotnet lambda package` works as expected
VM image for the pipeline: ubuntu-latest

Start with the LambdaNETCoreDeploy task and compare its packaging or build path with the reported working `dotnet lambda package` command. Reproduce the custom-feed restore on ubuntu-latest, then verify that the deployment package targets netcoreapp3.1 rather than Microsoft.NETCore.App 1.0.0.

Written by the indexing model from the issue text.