Disable flaky tests reported in #6574/#6644 (#6749)

Reference issues
#6574 
#6644

.gitlab/pipeline/zombienet/polkadot.yml

@@ -179,7 +179,7 @@ zombienet-polkadot-elastic-scaling-0001-basic-3cores-6s-blocks:
       --local-dir="${LOCAL_DIR}/elastic_scaling"
       --test="0001-basic-3cores-6s-blocks.zndsl"
 
-zombienet-polkadot-elastic-scaling-0002-elastic-scaling-doesnt-break-parachains:
+.zombienet-polkadot-elastic-scaling-0002-elastic-scaling-doesnt-break-parachains:
   extends:
     - .zombienet-polkadot-common
   before_script:
@@ -233,7 +233,7 @@ zombienet-polkadot-functional-0015-coretime-shared-core:
       --local-dir="${LOCAL_DIR}/functional"
       --test="0016-approval-voting-parallel.zndsl"
 
-zombienet-polkadot-functional-0017-sync-backing:
+.zombienet-polkadot-functional-0017-sync-backing:
   extends:
     - .zombienet-polkadot-common
   script: