Cirrus-CI: move QEMU pkg installation to test script

Occasionally the QEMU package fails to build and isn't available on
-CURRENT using the Latest package set.  Move the package installation
to the test script, so that if the package isn't available we at least
still perform a build test.

Sponsored by:	The FreeBSD Foundation

.cirrus.yml

@@ -31,7 +31,7 @@ task:
       TOOLCHAIN_PKG: amd64-gcc9
   timeout_in: 120m
   install_script:
-  - sh .cirrus-ci/pkg-install.sh qemu-nox11 ${TOOLCHAIN_PKG}
+  - sh .cirrus-ci/pkg-install.sh ${TOOLCHAIN_PKG}
   setup_script:
   - uname -a
   - df -m
@@ -44,6 +44,7 @@ task:
   package_script:
   - su user -c "make CROSS_TOOLCHAIN=${TOOLCHAIN_PKG} WITHOUT_TOOLCHAIN=yes PKG_FORMAT=tar packages"
   test_script:
+  - sh .cirrus-ci/pkg-install.sh qemu-nox11
   - sh tools/boot/ci-qemu-test.sh
   post_script:
   - df -m