Don't use preemptive agents for forwards compat tests

Author: mark-vieira

.buildkite/pipelines/periodic-fwc.template.yml

@@ -7,7 +7,6 @@ steps:
       image: family/elasticsearch-ubuntu-2004
       machineType: n1-standard-32
       buildDirectory: /dev/shm/bk
-      preemptible: true
     matrix:
       setup:
         FWC_VERSION: $FWC_LIST

.buildkite/pipelines/periodic-fwc.yml

@@ -1,16 +1,15 @@
 # This file is auto-generated. See .buildkite/pipelines/periodic-fwc.template.yml
 steps:
-  - label: "{{matrix.FWC_VERSION}} / fwc"
-    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
+  - label: $FWC_VERSION / fwc
+    command: .ci/scripts/run-gradle.sh -Dbwc.checkout.align=true v$FWC_VERSION#fwcTest -Dtests.bwc.snapshot=false
     timeout_in_minutes: 300
     agents:
       provider: gcp
       image: family/elasticsearch-ubuntu-2004
       machineType: n1-standard-32
       buildDirectory: /dev/shm/bk
-      preemptible: true
     matrix:
       setup:
         FWC_VERSION: []
     env:
-      FWC_VERSION: "{{matrix.FWC_VERSION}}"
+      FWC_VERSION: $FWC_VERSION