[Synthetics] Upgrade nodejs on CI to active LTS (#47168) (#47184)

Nodejs for Synthetics was upgraded on #47091,
which makes synthetics incompatible with the version running on CI.

Fixes: #47159


(cherry picked from commit 61bbfcc)

Co-authored-by: Marc Capell <[email protected]>
Co-authored-by: Emilio Alvarez Piñeiro <[email protected]>

Author: 3 people

.buildkite/heartbeat/heartbeat-pipeline.yml

@@ -20,7 +20,7 @@ env:
 
   # Other deps
   ASDF_MAGE_VERSION: 1.15.0
-  ASDF_NODEJS_VERSION: 18.17.1
+  ASDF_NODEJS_VERSION: 22.20.0
   ASDF_PYTHON_VERSION: 3.10.9
 
   # Unit tests

.buildkite/x-pack/pipeline.xpack.agentbeat.yml

@@ -181,7 +181,7 @@ steps:
         depends_on:
           - agentbeat-package-linux
         env:
-          ASDF_NODEJS_VERSION: 18.17.1
+          ASDF_NODEJS_VERSION: 22.20.0
           PLATFORMS: "+all linux/amd64 windows/amd64 darwin/amd64"
           SNAPSHOT: true
         command: |

.buildkite/x-pack/pipeline.xpack.heartbeat.yml

@@ -24,7 +24,7 @@ env:
 
   # Other deps
   ASDF_MAGE_VERSION: 1.15.0
-  ASDF_NODEJS_VERSION: 18.17.1
+  ASDF_NODEJS_VERSION: 22.20.0
 
   # Unit tests
   RACE_DETECTOR: "true"