ci: fix cmake install pipe issue and add install dir diagnostics

Remove pipe from cmake --install to properly propagate exit code.
Add directory listing before tar to diagnose missing install dir.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: zccrs

.github/workflows/dtkdeclarative-archlinux-build.yml

@@ -77,11 +77,13 @@ jobs:
 
       - name: Install dtkdeclarative to staging directory
         run: |
-          DESTDIR=/tmp/dtkdeclarative-install cmake --install build --verbose 2>&1 | tee /tmp/cmake-install.log || { echo "=== CMAKE INSTALL FAILED ==="; cat /tmp/cmake-install.log; exit 1; }
+          DESTDIR=/tmp/dtkdeclarative-install cmake --install build --verbose
           echo "Total: $(find /tmp/dtkdeclarative-install -type f | wc -l) files"
+          find /tmp/dtkdeclarative-install -type f | head -20
 
       - name: Create installation package
         run: |
+          ls -la /tmp/dtkdeclarative-install/ || { echo "Install dir missing!"; exit 1; }
           tar -czf /tmp/dtkdeclarative-archlinux-qt${{ matrix.qt_version }}-$(date +%Y%m%d-%H%M%S).tar.gz -C /tmp/dtkdeclarative-install .
           ls -la /tmp/dtkdeclarative-archlinux-qt${{ matrix.qt_version }}-*.tar.gz