CI - BUG FIX - Merge the duplicated env block in the test job

The multi-threaded matrix leg added JULIA_NUM_THREADS in a second `env:` key
alongside the existing DEPOT_PATHS one, so the test job carried a duplicate YAML
mapping key. GitHub rejects the whole workflow file on that, which is why no test
run reported on this branch and the required Tests context could never be
satisfied. Had it parsed, the later block would have won and dropped
JULIA_NUM_THREADS entirely, leaving the new leg single-threaded.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: d-burg

.github/workflows/test.yaml

@@ -95,8 +95,6 @@ jobs:
     if: needs.changes.outputs.julia == 'true'
     runs-on: ${{ matrix.os }}
     timeout-minutes: 90
-    env:
-      JULIA_NUM_THREADS: ${{ matrix.threads }}
     strategy:
       fail-fast: false
       matrix:
@@ -117,6 +115,7 @@ jobs:
             threads: '4'
 
     env:
+      JULIA_NUM_THREADS: ${{ matrix.threads }}
       DEPOT_PATHS: |
         ~/.julia/artifacts
         ~/.julia/packages