Cache parcagpu, hitting http egress limits

Author: gnurizen

.github/workflows/unit-test-on-pull-request.yml

@@ -292,6 +292,11 @@ jobs:
             *) echo >&2 "bug: bad arch selected"; exit 1;;
           esac
           sudo apt-get install -y debootstrap systemtap-sdt-dev
+      - name: Cache parcagpu library
+        uses: actions/cache@0400d5f644dc74513175e3cd8d07132dd4860809 # v4.2.4
+        with:
+          path: test/distro-qemu/parcagpu-lib
+          key: parcagpu-${{ matrix.target_arch }}
       - name: Download kernel
         run: |
           cd test/distro-qemu