Action started to fail

[ttarnowski]

The action doesn't seem to be working anymore, looks like an issue with dotnet/core container tags:

Build container for action use: '/home/githubrunner/actions-runner/_work/_actions/aliencube/microsoft-teams-actions/v0.8.0/Dockerfile'.
  /usr/bin/docker build -t [9](https://github.com/HavenEngineering/service-haven-activities-capacity/runs/6021805038?check_suite_focus=true#step:2:9)ec1c5:f4cd42253ece4b53ab93f84b1d9e8722 -f "/home/githubrunner/actions-runner/_work/_actions/aliencube/microsoft-teams-actions/v0.8.0/Dockerfile" "/home/githubrunner/actions-runner/_work/_actions/aliencube/microsoft-teams-actions/v0.8.0"
  Sending build context to Docker daemon  88.58kB
  
  Step 1 : FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build
  Error parsing reference: "mcr.microsoft.com/dotnet/core/sdk:3.1 AS build" is not a valid repository/tag
  Warning: Docker build failed with exit code 1, back off 9.483 seconds before retry.
  /usr/bin/docker build -t 9ec1c5:f4cd42253ece4b53ab93f84b1d9e8722 -f "/home/githubrunner/actions-runner/_work/_actions/aliencube/microsoft-teams-actions/v0.8.0/Dockerfile" "/home/githubrunner/actions-runner/_work/_actions/aliencube/microsoft-teams-actions/v0.8.0"
  Sending build context to Docker daemon  88.58kB
  
  Step 1 : FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build
  Error parsing reference: "mcr.microsoft.com/dotnet/core/sdk:3.1 AS build" is not a valid repository/tag
  Warning: Docker build failed with exit code 1, back off 1.85 seconds before retry.
  /usr/bin/docker build -t 9ec1c5:f4cd42253ece4b53ab93f84b1d9e8722 -f "/home/githubrunner/actions-runner/_work/_actions/aliencube/microsoft-teams-actions/v0.8.0/Dockerfile" "/home/githubrunner/actions-runner/_work/_actions/aliencube/microsoft-teams-actions/v0.8.0"
  Sending build context to Docker daemon  88.58kB
  
  Step 1 : FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build
  Error parsing reference: "mcr.microsoft.com/dotnet/core/sdk:3.1 AS build" is not a valid repository/tag
Error: Docker build failed with exit code 1

[riker09]

I assume this has something to do with the fact that Microsoft has deprecated these old Dotnet versions. Maybe an update to a still supported version would be enough? Unfortunately I don't have the time to try it myself

[ttarnowski]

Added the PR with Docker image URL change:
#19