common: clean up PMEM RAS workflow

- remove redundant matrix
- use `working-directory` syntax

Signed-off-by: Jan Michalski <jan.michalski@intel.com>

.github/workflows/pmem_ras.yml

@@ -34,11 +34,7 @@ jobs:
   linux:
     name: PMEM_RAS
     if: github.repository == 'pmem/pmdk'
-    runs-on: ${{ matrix.os }}
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [[self-hosted, ras_controller]]
+    runs-on: [self-hosted, ras_controller]
     env:
       WORKDIR: utils/gha-runners
 
@@ -50,15 +46,14 @@ jobs:
       # 'sed' command is used to filter out IP addresses from the ansible output, it will show up as the 'ras_runner' instead.
       # 'tee' command is used to save the overall output to the file. This file is needed for the next step.
       - name: Prepare and run RAS Linux tests via ansible-playbook
-        run: |
-          cd $WORKDIR
-          ansible-playbook -i $ras_runner, run-ras-linux.yml -e "host=all ansible_user=$ras_user" | sed 's/[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}/ras_runner/' | tee playbook_output.txt
+        working-directory: ${{ env.WORKDIR }}
+        run: ansible-playbook -i $ras_runner, run-ras-linux.yml -e "host=all ansible_user=$ras_user" | sed 's/[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}/ras_runner/' | tee playbook_output.txt
 
       # This simple step will look through the output in search of specific fail strings.
-      # If any phrase is found in the file, the workflow will fail.
+      # The workflow will fail if any of the expected phrases are found in the file.
       - name: Fail the workflow if the playbook finished with a failure
+        working-directory: ${{ env.WORKDIR }}
         run: |
-          cd $WORKDIR
           if grep -E 'fatal: \[ras_runner\]: FAILED!|failed: \[ras_runner\]' "playbook_output.txt"; then
             exit 1
           else