CI: pass DYNAMIC to stage1 build to fix dynHelloWorld test failure

When stage1 is built without DYNAMIC but stage2 with DYNAMIC=1,
config.status is created without --enable-dynamic. This means
cabal.project.stage2.settings gets shared: False, so no dynamic
libraries are built. However, the stage1 recipe re-runs during
stage2 (order-only dep on non-file target) with DYNAMIC=1, causing
the sed to add 'dyn' to RTS ways in settings. Result: settings
claims dyn is available but no .dylib/.so files exist, causing
dynHelloWorld(dyn) to fail on darwin.

Fix: pass DYNAMIC=${{ matrix.dynamic }} to stage1 so configure
runs with --enable-dynamic from the start, generating the correct
cabal.project.stage2.settings with shared: True.

Author: angerman

.github/workflows/nix-ci.yml

@@ -136,7 +136,7 @@ jobs:
         export CABAL_DIR="$GITHUB_WORKSPACE/_build/cabal-dir"
         export TMPDIR="$GITHUB_WORKSPACE/_build/tmp"
         mkdir -p "$TMPDIR"
-        make QUIET=1 CABAL_ARGS="-j2" ${{ steps.cabal-cache.outputs.cache-hit == 'true' && 'USE_SYSTEM_CABAL=1' || '' }} stage1
+        make QUIET=1 DYNAMIC=${{ matrix.dynamic }} CABAL_ARGS="-j2" ${{ steps.cabal-cache.outputs.cache-hit == 'true' && 'USE_SYSTEM_CABAL=1' || '' }} stage1
         echo "=== Disk after stage1 ==="
         df -h .