[ISSUE]: Overwriting readonly variable 'GitVersion.Major' is not permitted

[jochenjonc]

Prerequisites

• I have written a descriptive issue title
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GitVersion package

AzureDevops task

What are you seeing?

Since the last update, all build using GitVersion are broken with the following error:

##[error]Unable to process command '##vso[task.setvariable variable=GitVersion.Major]5' successfully. Please reference documentation (http://go.microsoft.com/fwlink/?LinkId=817296)
##[error]Overwriting readonly variable 'GitVersion.Major' is not permitted. See https://github.com/microsoft/azure-pipelines-yaml/blob/master/design/readonly-variables.md for details.

It seems that changes in #1343 are executing the GitVersion tool twice and the second time it tries to overwrite the readonly variables that were set in the first run.

What is expected?

It's expected that GitVersion is only run once.

Steps to Reproduce

Make sure to run GitVersion with the latest version:

    - task: gitversion/setup@3.0.2
      displayName: 'Install GitVersion'
      inputs:
        versionSpec: '6.x'

    - task: gitversion/execute@3.0.2
      displayName: 'Determine application version with GitVersion'
      name: GitVersion

Output log or link to your CI build (if appropriate).

Starting: Determine application version with GitVersion
==============================================================================
Task         : Execute GitVersion Task
Description  : Easy Semantic Versioning (https://semver.org) for projects using Git
Version      : 3.0.2
Author       : GitTools Contributors
Help         : See the [documentation](https://gitversion.net/docs/) for help
==============================================================================
Running on: 'Azure Pipelines'
Disable Telemetry
Executing GitVersion
Command: git -C /home/vsts/work/1/s rev-parse --is-shallow-repository
Command: /opt/hostedtoolcache/GitVersion.Tool/6.0.5/dotnet-gitversion /home/vsts/work/1/s /output json /output buildserver /config /home/vsts/work/1/s/GitVersion.yml
GitVersion executed successfully
GitVersion output:
...
Executing GenerateSetVersionMessage for 'AzurePipelines'.
Executing GenerateBuildLogOutput for 'AzurePipelines'.
...

-------------------
GitVersion executed successfully
...
Executing GenerateSetVersionMessage for 'AzurePipelines'.
Executing GenerateBuildLogOutput for 'AzurePipelines'.
##[error]Unable to process command '##vso[task.setvariable variable=GitVersion.Major]5' successfully. Please reference documentation (http://go.microsoft.com/fwlink/?LinkId=817296)
##[error]Overwriting readonly variable 'GitVersion.Major' is not permitted. See https://github.com/microsoft/azure-pipelines-yaml/blob/master/design/readonly-variables.md for details.
...