Bump netinst images to 3GiB RAM (#1856514)

Since systemd-246~rc1-1.fc33, network install images crash if
booted with only 2GiB of RAM. No-one seems to be fixing this
as a matter of urgency, so let's just bump the tests to 3GiB at
least for now.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

templates.fif.json

@@ -129,6 +129,7 @@
             "distri": "fedora",
             "flavor": "Everything-boot-iso",
             "settings": {
+                "QEMURAM": 3072,
                 "TEST_TARGET": "ISO"
             },
             "version": "*"
@@ -199,6 +200,7 @@
             "distri": "fedora",
             "flavor": "Server-boot-iso",
             "settings": {
+                "QEMURAM": 3072,
                 "TEST_TARGET": "ISO"
             },
             "version": "*"