do not trigger zombienet workflows on 'labeled' (#9427)

At some point of the stabilization process we added the 'labeled' to the
list of events that trigger the zombienet workflows. This is not needed
anymore and also is causing failures because the _artifacts_ could be
expired
([example](https://github.com/paritytech/polkadot-sdk/actions/runs/16529272288/job/46752021278?pr=9286#step:6:127)).

Thx!

Author: pepoviola

.github/workflows/zombienet_cumulus.yml

@@ -12,7 +12,7 @@ on:
    branches:
      - master
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review, labeled]
+    types: [opened, synchronize, reopened, ready_for_review]
   merge_group:
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}

.github/workflows/zombienet_parachain-template.yml

@@ -12,7 +12,7 @@ on:
    branches:
      - master
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review, labeled]
+    types: [opened, synchronize, reopened, ready_for_review]
   merge_group:
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}

.github/workflows/zombienet_polkadot.yml

@@ -12,7 +12,7 @@ on:
    branches:
      - master
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review, labeled]
+    types: [opened, synchronize, reopened, ready_for_review]
   merge_group:
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}

.github/workflows/zombienet_substrate.yml

@@ -12,7 +12,7 @@ on:
    branches:
      - master
   pull_request:
-    types: [opened, synchronize, reopened, ready_for_review, labeled]
+    types: [opened, synchronize, reopened, ready_for_review]
   merge_group:
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}