Deduplicate S3 publishing determination code in build workflow

The "Arduino IDE" GitHub Actions workflow uploads the nightly and release builds to Amazon S3, from which they are
downloaded by the auto-update as well as directly by users via the links on the "Software" page of arduino.cc.

The workflow can also be useful in forks. Either by those who want to test contributions staged in their fork prior to
submitting a PR to the parent repo, or by those maintaining a hard fork of the project. Even though these forks wouldn't
(and couldn't due to lack of access to the encrypted credential secrets only available to the workflow when ran in a
trusted context in Arduino's repo)credentials stored in Arduino's repo) use the S3 upload component of the workflow,
they may still find it valuable for continuous integration as well as continuous deployment via the tester builds and
release builds the workflow also publishes to the GitHub repository it runs in. For this reason, the workflow contains
code to determine whether it should attempt the S3 uploads. Previously that code was duplicated in both the nightly and
release publishing jobs of the workflow. Since the workflow already contains a job specifically for the purpose of
determining the characteristics of the build being performed and making that information available from single source
for use throughout the rest of the workflow, it makes sense to also move the S3 upload determination code to that job.

.github/workflows/build.yml

@@ -136,6 +136,7 @@ jobs:
       is-release: ${{ steps.determination.outputs.is-release }}
       is-nightly: ${{ steps.determination.outputs.is-nightly }}
       channel-name: ${{ steps.determination.outputs.channel-name }}
+      publish-to-s3: ${{ steps.determination.outputs.publish-to-s3 }}
     permissions: {}
     steps:
       - name: Determine the type of build
@@ -166,6 +167,8 @@ jobs:
           echo "is-release=$is_release" >> $GITHUB_OUTPUT
           echo "is-nightly=$is_nightly" >> $GITHUB_OUTPUT
           echo "channel-name=$channel_name" >> $GITHUB_OUTPUT
+          # Only attempt upload to Amazon S3 if the credentials are available.
+          echo "publish-to-s3=${{ github.repository == 'arduino/arduino-ide' }}" >> $GITHUB_OUTPUT
 
   select-targets:
     needs: build-type-determination
@@ -509,7 +512,7 @@ jobs:
       - merge-channel-files-complete
       - changelog
     if: >
-      github.repository == 'arduino/arduino-ide' &&
+      needs.build-type-determination.outputs.publish-to-s3 == 'true' &&
       needs.build-type-determination.outputs.is-nightly == 'true'
     runs-on: ubuntu-latest
     steps:
@@ -566,7 +569,7 @@ jobs:
           rm "${{ env.JOB_TRANSFER_ARTIFACT }}/stable-linux.yml"
 
       - name: Publish Release [S3]
-        if: github.repository == 'arduino/arduino-ide'
+        if: needs.build-type-determination.outputs.publish-to-s3 == 'true'
         uses: docker://plugins/s3
         env:
           PLUGIN_SOURCE: '${{ env.JOB_TRANSFER_ARTIFACT }}/*'