fix(workflow): correct legacy compiler selection in test-legacy-upgrade.yaml

- Replace `head -n 2` with `sed -n 2p` for accurate selection of the second compiler

Author: CoMfUcIoS

.github/workflows/test-legacy-upgrade.yaml

@@ -174,7 +174,7 @@ jobs:
           echo ::group::get_peadm_config
           primary=$(yq '.groups[].targets[] | select(.vars.role == "primary") | .name' spec/fixtures/litmus_inventory.yaml)
           compiler=$(yq '.groups[].targets[] | select(.vars.role == "compiler") | .name' spec/fixtures/litmus_inventory.yaml | head -n 1)
-          legacy_compiler=$(yq '.groups[].targets[] | select(.vars.role == "compiler") | .name' spec/fixtures/litmus_inventory.yaml | head -n 2)
+          legacy_compiler=$(yq '.groups[].targets[] | select(.vars.role == "compiler") | .name' spec/fixtures/litmus_inventory.yaml | sed -n 2p)
           bundle exec bolt task run peadm::get_peadm_config \
             --targets $primary \
             --inventoryfile spec/fixtures/litmus_inventory.yaml \