Specify the full path for pip3

Ensure that we are using the system pip. This both aligns with what we
do in other roles and the needs of the cisagov/cyhy-runner package and
the configuration in this role.

Author: mcdonnnj

tasks/main.yml

@@ -16,7 +16,7 @@
 
 - name: Install the cyhy-runner package
   ansible.builtin.pip:
-    executable: pip3
+    executable: /usr/bin/pip3
     # The extra argument is necessary on modern platforms, which
     # correctly recognize that the local Python is externally managed
     # (i.e. managed via the system package manager and not by pip).