[CI][Benchmarks] Fix pushing results to new branch (#20544)

There is a bug that results in Nightly Benchmarks to fail pushing new
results to the new results branch on `intel/llvm`:
```
[sycl d0defc8] [GHA] Upload compute-benchmarks results from https://github.com/intel/llvm/actions/runs/19053464326
 2 files changed, 15321 insertions(+)
 create mode 100644 data.json
 create mode 100644 results/Baseline_BMG_L0v2_20251104_003023.json
remote: error: GH006: Protected branch update failed for refs/heads/sycl.        
remote: 
remote: - Changes must be made through a pull request.        
remote: 
remote: - You're not authorized to push to this branch. Visit https://docs.github.com/repositories/configuring-branches-and-merges-in-your-repository/managing-protected-branches/about-protected-branches for more information.  
```
This patch fixes the benchmarking workflow to properly push to the
correct
[sycl-benchmark-ci-results](https://github.com/intel/llvm/tree/sycl-benchmark-ci-results)
branch.

Author: PatKamin

devops/actions/run-tests/benchmark/action.yml

@@ -37,9 +37,6 @@ inputs:
     type: string
     required: False
 
-env:
-  BENCHMARK_RESULTS_BRANCH: "sycl-benchmark-ci-results"
-
 runs:
   # composite actions don't make use of 'name', so copy-paste names as a comment in the first line of each step
   using: "composite"
@@ -164,6 +161,14 @@ runs:
       sudo cmake --install build
 
       cd -
+  - name: Set env var for results branch
+    shell: bash
+    run: |
+        # Set env var for results branch
+        # Set BENCHMARK_RESULTS_BRANCH globally for all subsequent steps.
+        # This has to be done this way because of limits of composite actions.
+        BENCHMARK_RESULTS_BRANCH="sycl-benchmark-ci-results"
+        echo "BENCHMARK_RESULTS_BRANCH=$BENCHMARK_RESULTS_BRANCH" >> $GITHUB_ENV
   - name: Checkout results repo
     uses: actions/checkout@v5
     with: