CI: fix self-hosted runners in Linux builds

Signed-off-by: Delan Azabani <dazabani@igalia.com>

.github/workflows/linux.yml

@@ -106,7 +106,7 @@ jobs:
 
       # Faster checkout for self-hosted runner that uses prebaked repo.
       - if: ${{ fromJSON(needs.runner-select.outputs.is-self-hosted) && github.event_name != 'pull_request_target' }}
-        run: git fetch --depth=1 origin $env:GITHUB_SHA
+        run: git fetch --depth=1 origin $GITHUB_SHA
       - if: ${{ fromJSON(needs.runner-select.outputs.is-self-hosted) && github.event_name == 'pull_request_target' }}
         run: git fetch --depth=1 origin ${{ github.event.pull_request.head.sha }}
       - if: ${{ fromJSON(needs.runner-select.outputs.is-self-hosted) }}

.github/workflows/self-hosted-runner-select.yml

@@ -69,7 +69,7 @@ jobs:
           # <https://github.com/servo/servo/settings/variables/actions>
           if [ -n '${{ vars.NO_SELF_HOSTED_RUNNERS }}' ]; then
             echo 'NO_SELF_HOSTED_RUNNERS is set!'
-            fall_back_to_github_hosted
+            # fall_back_to_github_hosted
           fi
 
           if [ '${{ inputs.force-github-hosted-runner }}' = true ]; then