Update on "[build] Add editable mode unittest"

As titled. To do this we need to refactor the arguments being passed
into `setup-linux.sh` `setup-macos.sh` and `unittest-linux.sh`
`unittest-macos.sh`.

[ghstack-poisoned]

Author: larryliu0820

.ci/scripts/setup-linux.sh

@@ -15,10 +15,10 @@ parse_args "$@"
 # As Linux job is running inside a Docker container, all of its dependencies
 # have already been installed, so we use PyTorch build from source here instead
 # of nightly. This allows CI to test against latest commits from PyTorch
-if [[ "$EDITABLE" == "true" ]]; then
-  install_executorch "--use-pt-pinned-commit" "--editable"
+if [[ "${EDITABLE:-false}" == "true" ]]; then
+  install_executorch --use-pt-pinned-commit --editable
 else
-  install_executorch "--use-pt-pinned-commit"
+  install_executorch --use-pt-pinned-commit
 fi
 build_executorch_runner "${BUILD_TOOL}" "${BUILD_MODE}"
 

.github/workflows/_unittest.yml

@@ -18,7 +18,7 @@ on:
       editable:
         required: false
         type: string
-        description: Install ExecuTorch in editable or not.
+        description: Install ExecuTorch in editable mode or not.
       python-version:
         required: false
         type: string