ci: more complete workaround for actions/partner-runner-images#25

From <actions/partner-runner-images#25 (comment)>.
Adapted to edit both variables.

.github/workflows/build.yml

@@ -83,6 +83,11 @@ jobs:
     outputs:
       nurRepo: ${{ steps.build.outputs.nurRepo }}
     steps:
+    - name: Fix PATH and XDG_CONFIG_HOME for ARM64 Linux runners (actions/partner-runner-images#25)
+      if: ${{ startsWith(matrix.runner, 'ubuntu-') && endsWith(matrix.runner, '-arm') }}
+      # From <https://github.com/actions/partner-runner-images/issues/25#issuecomment-2597256482>.
+      # Adapted to edit both variables.
+      run: for var in PATH XDG_CONFIG_HOME; do sed -Ee "s/^/${var}=/" -e 's/(runner)admin/\1/g' <<< "${!var}"; done | tee -a "$GITHUB_ENV"
     - name: Output nurRepo for final job
       run: echo 'nurRepo=${{ matrix.nurRepo }}' >> "$GITHUB_OUTPUT"
     - name: Checkout repository
@@ -110,8 +115,6 @@ jobs:
         name: ${{ matrix.cachixName }}
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
         authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-      env:
-        XDG_CONFIG_HOME: ~/.config
     - name: Check evaluation
       run: |
         nix-env -f . -qa \* --meta --xml \