Try to work around workflow YAML env setting limitation.

.github/workflows/build.yaml

@@ -13,7 +13,22 @@ env:
   RELEASE_RUN: ${{ github.ref_type == 'tag' && startsWith(github.ref_name, 'Second_Life') && 'Y' }}
 
 jobs:
+  # The whole point of the setvar job is that we want to reference global
+  # env.RELEASE_RUN in build.env, but a job.env can't directly reference the
+  # global env context.
+  setvar:
+    runs-on: ubuntu-latest
+    outputs:
+      release_run: ${{ steps.setvar.outputs.release_run }}
+    steps:
+      - name: Set Variable
+        id: setvar
+        shell: bash
+        run: |
+          echo "release_run=$RELEASE_RUN" >> "$GITHUB_OUTPUT"
+
   build:
+    needs: setvar
     strategy:
       matrix:
         runner: [windows-large, macos-12-xl]
@@ -49,7 +64,7 @@ jobs:
       BUGSPLAT_DB: ${{ matrix.Linden && 'SecondLife_Viewer_2018' || '' }}
       # Run BUILD steps for Release configuration.
       # Run BUILD steps for ReleaseOS configuration only for release runs.
-      BUILD: ${{ (matrix.Linden || env.RELEASE_RUN) && 'Y' || '' }}
+      BUILD: ${{ (matrix.Linden || needs.setvar.outputs.release_run) && 'Y' || '' }}
       build_coverity: false
       build_log_dir: ${{ github.workspace }}/.logs
       build_viewer: true