Update tier0 test plans environment vars

Set LEAPP_UNSUPPORTED and LEAPP_DEVEL_SKIP_CHECK_OS_RELEASE to 1,
becuase currently upgrade from 9.7 to 10.1 is unsuppported at this
phase of development and it will be allowed later.

It's expected to drop this two variables for the final builds.

plans/tier0.fmf

@@ -7,6 +7,8 @@ summary: Internal Tier0 tests
 environment:
     SOURCE_RELEASE: '9.7'
     TARGET_RELEASE: '10.1'
+    LEAPP_UNSUPPORTED: '1'
+    LEAPP_DEVEL_SKIP_CHECK_OS_RELEASE: '1'
 
 context:
     distro: rhel-9.7