Sets SOF root source directory in workflow environment

Defines the SOF_ROOT_SOURCE_DIRECTORY environment variable in the GitHub Actions workflow to standardize the root source directory path for builds.

Improves build consistency and simplifies configuration.

Signed-off-by: Christopher Turner <christopher.g.turner@intel.com>

Author: cgturner1

.github/workflows/testbench.yml

@@ -32,6 +32,8 @@ jobs:
 
   build-run:
     runs-on: ubuntu-22.04
+    env:
+      SOF_ROOT_SOURCE_DIRECTORY: /home/sof/work/sof.git
 
     steps:
       - uses: actions/checkout@v4