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

Reference issues
paritytech#6574 
paritytech#6644

Author: pepoviola

.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: