Rename TEST_MODE to specific variable for CodeQL Action

This allows us to set it automatically in the workflow generator,
simplifying things and reducing the scope for error.

.github/workflows/__split-workflow.yml

@@ -54,8 +54,6 @@ jobs:
         packs: +dsp-testing/codeql-pack1@1.0.0
         languages: javascript
         tools: ${{ steps.prepare-test.outputs.tools-url }}
-      env:
-        TEST_MODE: true
     - name: Build code
       shell: bash
       run: ./build.sh
@@ -63,8 +61,6 @@ jobs:
       with:
         skip-queries: true
         output: ${{ runner.temp }}/results
-      env:
-        TEST_MODE: true
 
     - name: Assert No Results
       shell: bash
@@ -77,8 +73,6 @@ jobs:
       with:
         output: ${{ runner.temp }}/results
         upload-database: false
-      env:
-        TEST_MODE: true
     - name: Assert Results
       shell: bash
       run: |
@@ -95,3 +89,4 @@ jobs:
         fi
     env:
       INTERNAL_CODEQL_ACTION_DEBUG_LOC: true
+      CODEQL_ACTION_TEST_MODE: true