fix(workflow): correct yq command in test-upgrade-legacy job

- Redirect bolt task output to a file for yq processing
- Ensure accurate extraction of legacy_compiler from peadm_config.json

Author: CoMfUcIoS

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

@@ -128,7 +128,8 @@ jobs:
         run: |
           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 '.items[0].value.params.legacy_compilers[0]' bolt task run peadm::get_peadm_config -t $primary --no-host-key-check --format json)
+          bolt task run peadm::get_peadm_config -t $primary --no-host-key-check --format json > peadm_config.json
+          legacy_compiler=$(yq '.items[0].value.params.legacy_compilers[0]' peadm_config.json)
           if [ "$compiler" != "$legacy_compiler" ]; then
             echo "Compiler conversion failed"
             exit 1