ci: build only libunbound on linux

monero only needs the library, but the step built the daemon and the tools
too, serially. Build and install just the library, which takes about a
tenth of the time. It installs unbound.h, libunbound.a, libunbound.la and
libunbound.pc, everything FindUnbound looks for.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Author: everoddandeven

.github/workflows/test.yml

@@ -70,8 +70,9 @@ jobs:
           tar xzf unbound-1.22.0.tar.gz
           cd unbound-1.22.0
           ./configure --with-libexpat=/usr/local --with-ssl=/usr --enable-static --disable-shared --with-pic
-          make
-          sudo make install
+          # monero only needs libunbound, skip the daemon and the tools
+          make -j"$(nproc)" lib
+          sudo make install-lib
           cd ../
 
       - name: Restore ccache