refactor(ci): drop dead discover passthrough job in package-testing

package-testing.yml has no workflow_call trigger and no external callers,
so the 'backwards-compat passthrough' justification in the discover job
comment did not hold. The job consumed a full runner slot just to echo
config.outputs.package-extras into its own output — pure overhead.

Remove the discover job and have package-variants consume
needs.config.outputs.package-extras directly.  The matrix fromJSON
expression and all downstream jobs are unaffected; they already
referenced config for python-versions and default-python-version.

Author: fgogolli

.github/workflows/package-testing.yml

@@ -32,37 +32,20 @@ jobs:
     name: Get Configuration
     uses: ./.github/workflows/shared-config.yml
 
-  # Legacy discovery job kept for backwards-compat with any callers that may
-  # reference this workflow's outputs directly.  The package-extras value is
-  # now sourced from config (shared-config) above; this job is a no-op passthrough.
-  discover:
-    name: Discover Package Extras
-    runs-on: ubuntu-latest
-    needs: [config]
-    permissions:
-      contents: read
-    outputs:
-      package-extras: ${{ steps.passthrough.outputs.package-extras }}
-    steps:
-      - name: Pass through package-extras from shared config
-        id: passthrough
-        run: |
-          echo "package-extras=${{ needs.config.outputs.package-extras }}" >> "$GITHUB_OUTPUT"
-
   package-variants:
     name: Test Package Variants
     runs-on: ubuntu-latest
-    needs: [config, discover]
+    needs: [config]
     permissions:
       contents: read
     strategy:
       fail-fast: false
       matrix:
-        # Dynamic: fromJSON pulls the discovered extras list.
+        # Dynamic: fromJSON pulls the discovered extras list from shared-config.
         # The 'minimal' base install (no extras) is always tested first via a
         # separate include entry so the matrix only needs extra names here.
         # Static fallback ['cli','api','monitoring'] preserves historical coverage.
-        extra: ${{ fromJSON(needs.discover.outputs.package-extras || '["cli","api","monitoring"]') }}
+        extra: ${{ fromJSON(needs.config.outputs.package-extras || '["cli","api","monitoring"]') }}
         # Python version axis driven from .project.yml via shared-config.
         # Static fallback keeps act/offline CI valid; update it when python.versions changes.
         python-version: ${{ fromJSON(needs.config.outputs.python-versions || '["3.10", "3.11", "3.12", "3.13", "3.14"]') }}