run banner exec test only for NXOS7K (#29041)

Signed-off-by: Trishna Guha <trishnaguha17@gmail.com>

test/integration/targets/nxos_banner/tests/common/basic-exec.yaml

@@ -1,4 +1,7 @@
 ---
+- debug: msg="START nxos_banner exec test"
+
+- block:
     - name: setup - remove exec
       nxos_banner:
         banner: exec
@@ -30,6 +33,10 @@
           - "result.changed == false"
           - "result.commands | length == 0"
 
+  when: platform | match("N7K")
+
+- debug: msg="END nxos_banner exec test"
+
 # FIXME add in tests for everything defined in docs
 # FIXME Test state:absent + test:
 # FIXME Without powers ensure "privileged mode required"