frome: Install bash, needed by ssl-cert

The `make-ssl-cert` script specifically targets bash, so let's install it
explicitly.

The `ssl-cert` package is brought in by `postfix`, which is needed by `quilt`,
suggested by `devscript`.

This fixes the error below:
    Setting up ssl-cert (1.0.39ba1) ...
    /var/lib/dpkg/info/ssl-cert.postinst: 48: /var/lib/dpkg/info/ssl-cert.postinst: make-ssl-cert: not found
    dpkg: error processing package ssl-cert (--configure):
     installed ssl-cert package post-installation script subprocess returned error exit status 127

The install error also caused the subsequent tests to be skipped due to the
inconsistent state.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

test-cases/frome.yaml

@@ -24,6 +24,7 @@ metadata:
 
 install:
   deps:
+    - bash
     - devscripts
     - frome-tests
     - gnome-desktop-testing