Cirrus: Utilize $GOPATH cache for alt_build task

Specifically, the result of 'make install.tools' is needed.  Part of
that target installs tooling into `$GOPATH/bin`.  A future commit
requires this tooling for the `Build Each Commit` item of the
alt_build matrix.  Re-use the cache of this directory for this
task to ensure the necessary tooling/libraries are available.

Signed-off-by: Chris Evich <cevich@redhat.com>

.cirrus.yml

@@ -317,6 +317,8 @@ alt_build_task:
             ALT_NAME: 'Test build RPM'
       - env:
             ALT_NAME: 'Alt Arch. Cross'
+    gopath_cache: *ro_gopath_cache
+    clone_script: *noop  # Comes from cache
     setup_script: *setup
     main_script: *main
     always: *binary_artifacts