ci(github): fix conditionals in matrix of asset-exchange-besu-local

The file affected is this one:
`.github/workflows/test_weaver-asset-exchange-besu.yaml`

The if conditions have to be implemented in a different syntax for jobs
that use the `matrix` feature of GitHub Action workflows so a slight
refactor has been done to make the code do what we originally wanted it to.

The fix was heavily inspired by this excellent answer on StackOverflow:
https://stackoverflow.com/a/73822998

```yaml
strategy:
  matrix:
    fruits:
      - apple
      - banana
    exclude:
      - fruits: ${{ github.ref == 'refs/heads/main' && 'dummy' || 'apple' }}
```

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

.github/workflows/test_weaver-asset-exchange-besu.yaml

@@ -220,14 +220,15 @@ jobs:
 
   asset-exchange-besu-local:
     needs: check_code_changed
-    if: needs.check_code_changed.outputs.status == 'true'
     # The type of runner that the job will run on
     runs-on: ubuntu-latest
 
     strategy:
       fail-fast: false
       matrix:
         app_contract: ["AliceERC1155", "AliceERC20", "AliceERC721"]
+        exclude:
+          - app_contract: ${{ needs.check_code_changed.outputs.status != 'true' }}
 
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps: