chromium_tests: use correct cwd for analyze diff

scripts/slave/recipes/chromium_trybot.expected/full_tryserver_chromium_win_win_clang.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_PACKAGE_REPO[build]\\scripts\\slave\\kill_processes.py"
     ],
     "name": "taskkill"
   },
   {
@@ skipping 256 matching lines @@
     "cwd": "RECIPE_PACKAGE_REPO[depot_tools]",
     "name": "ensure git tooling on windows"
   },
   {
     "cmd": [
       "RECIPE_PACKAGE_REPO[depot_tools]\\git.bat",
       "diff",
       "--cached",
       "--name-only"
     ],
-    "cwd": "[SLAVE_BUILD]\\src",
+    "cwd": "[BUILDER_CACHE]\\win_clang\\src",
     "name": "git diff to analyze patch",
     "stdout": "/path/to/tmp/",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@files@foo.cc@@@",
       "@@@STEP_LOG_END@files@@@",
       "@@@SET_BUILD_PROPERTY@subproject_tag@\"chromium\"@@@"
     ]
   },
   {
     "cmd": [
@@ skipping 159 matching lines @@
       "import sys; sys.exit(0)"
     ],
     "name": "mark: before_tests"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]