[CI] Use only RFSoC4x2 board for now

Author: fpjentzsch

ci/.gitlab-bench.yml

@@ -58,6 +58,7 @@ Measurement:
   stage: measure
   tags:
     - board
+    - rfsoc4x2
   rules:
     # Also run on failure of previous tasks to measure partial results
     - when: always
@@ -162,6 +163,7 @@ Measurement (Follow-up):
     - job: FINN Build (Follow-up)
   tags:
     - board
+    - rfsoc4x2
   script:
     # Check if follow-up build artifacts exist, exit gracefully if not
     - |