COMP: Fix "ci" GitHub workflow ensuring Slicer package is uploaded

[jcfr]

Set the step id to slicer-build to ensure the use of ${{ steps.slicer-build.outputs.package }} in the Upload Slicer package step effectively lookup the package.

Follow up of these pull requests:

• COMP: Add "CI" GitHub action workflow to replace CircleCI #6051
• COMP: Improve "CI" GitHub Action workflow uploading package as artifact #6053

Also fix the following warning:

The set-output command is deprecated and will be disabled soon.
Please upgrade to using Environment Files.
For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

Temporarily including the following patch to the pull-request allowed to test the changes:

diff --git a/.github/actions/slicer-build/entrypoint.sh b/.github/actions/slicer-build/entrypoint.sh
index 2caf49c7f02..50e709c8579 100755
--- a/.github/actions/slicer-build/entrypoint.sh
+++ b/.github/actions/slicer-build/entrypoint.sh
@@ -6,13 +6,16 @@ set -o
 
 cp -r $GITHUB_WORKSPACE /usr/src/Slicer
 
-/usr/src/Slicer-build/BuildSlicer.sh
-package_filepath=$(head -n1 /usr/src/Slicer-build/Slicer-build/PACKAGE_FILE.txt)
+#/usr/src/Slicer-build/BuildSlicer.sh
+#package_filepath=$(head -n1 /usr/src/Slicer-build/Slicer-build/PACKAGE_FILE.txt)
+package_filepath=/usr/src/Slicer-build/Slicer-build/Slicer-5.5.0-2023-09-26-linux-amd64.tar.gz
+echo "Dummy package" > $package_filepath
 echo "package_filepath [${package_filepath}]"
 
 mv ${package_filepath} $GITHUB_WORKSPACE/
 
 package=$(basename $package_filepath)
 echo "package [${package}]"
+echo "GITHUB_OUTPUT [$GITHUB_OUTPUT]"
 
 echo "package=$package" >> $GITHUB_OUTPUT

and confirm it was working as expected:

[sjh26]

lgtm