Building on self-hosted Windows 10: Failed to run "sh "

Hey!

**Bug description**
I am trying to set up a build pipeline, and since we have a lot of spare Windows 10 workstations around, I felt it would be a good use for them to be part of a build farm.

Unfortunately, it seems that there is a problem, please review the information below:

OS: Windows 10 64bit

**Configuration**
```
- uses: game-ci/unity-builder@v2
env:
UNITY_EMAIL: ${{ secrets.UNITY_EMAIL }}
UNITY_PASSWORD: ${{ secrets.UNITY_PASSWORD }}
UNITY_SERIAL: ${{ secrets.UNITY_SERIAL }}
with:
unityVersion: '2019.2.17f1'
targetPlatform: StandaloneWindows
```

**Error Log**
```
##[debug]Evaluating: secrets.UNITY_EMAIL
##[debug]Evaluating Index:
##[debug]..Evaluating secrets:
##[debug]..=> Object
##[debug]..Evaluating String:
##[debug]..=> 'UNITY_EMAIL'
##[debug]=> '***'
##[debug]Result: '***'
##[debug]Evaluating: secrets.UNITY_PASSWORD
##[debug]Evaluating Index:
##[debug]..Evaluating secrets:
##[debug]..=> Object
##[debug]..Evaluating String:
##[debug]..=> 'UNITY_PASSWORD'
##[debug]=> '***'
##[debug]Result: '***'
##[debug]Evaluating: secrets.UNITY_SERIAL
##[debug]Evaluating Index:
##[debug]..Evaluating secrets:
##[debug]..=> Object
##[debug]..Evaluating String:
##[debug]..=> 'UNITY_SERIAL'
##[debug]=> '***'
##[debug]Result: '***'
##[debug]Evaluating condition for step: 'Run game-ci/unity-builder@v2'
##[debug]Evaluating: success()
##[debug]Evaluating success:
##[debug]=> true
##[debug]Result: true
##[debug]Starting: Run game-ci/unity-builder@v2
##[debug]Loading inputs
##[debug]Loading env
Run game-ci/unity-builder@v2
with:
unityVersion: 2019.2.17f1
targetPlatform: StandaloneWindows
versioning: Semantic
androidAppBundle: false
awsBaseStackName: game-ci
cloudRunnerCluster: local
cloudRunnerCpu: 1.0
cloudRunnerMemory: 750M
kubeVolumeSize: 5Gi
env:
UNITY_EMAIL: ***
UNITY_PASSWORD: ***
UNITY_SERIAL: ***
Warning:
Library folder does not exist.
Consider setting up caching to speed up your workflow,
if this is not your first build.

##[debug]exec tool: C:\Program Files\Git\cmd\git.exearguments: rev-parse --is-shallow-repositoryExit code 0 received from tool 'C:\Program Files\Git\cmd\git.exe'STDIO streams have closed for tool 'C:\Program Files\Git\cmd\git.exe'
true

##[debug]exec tool: C:\Program Files\Git\cmd\git.exearguments: fetch --unshallowExit code 0 received from tool 'C:\Program Files\Git\cmd\git.exe'STDIO streams have closed for tool 'C:\Program Files\Git\cmd\git.exe'

Error: Failed to run "sh ".
In-command error caught: Error: Unable to locate executable file: sh. Please verify either the file path exists or the file can be found within a directory specified by the PATH environment variable. Also verify the file has a valid extension for an executable file.
##[debug]Node Action run completed with exit code 1
##[debug]Finishing: Run game-ci/unity-builder@v2```