ci: store fake DD_API_KEY as a secret (#11690)

Author: brettlangdon

.github/workflows/system-tests.yml

@@ -54,7 +54,7 @@ jobs:
       # system-tests requires an API_KEY, but it does not have to be a valid key, as long as we don't run a scenario
       # that make assertion on backend data. Using a fake key allow to run system tests on PR originating from forks.
       # If ever it's needed, a valid key exists in the repo, using ${{ secrets.DD_API_KEY }}
-      DD_API_KEY: 1234567890abcdef1234567890abcdef
+      DD_API_KEY: ${{ secrets.FAKE_DD_API_KEY }}
       CMAKE_BUILD_PARALLEL_LEVEL: 12
       SYSTEM_TESTS_AWS_ACCESS_KEY_ID: ${{ secrets.IDM_AWS_ACCESS_KEY_ID }}
       SYSTEM_TESTS_AWS_SECRET_ACCESS_KEY: ${{ secrets.IDM_AWS_SECRET_ACCESS_KEY }}
@@ -106,7 +106,7 @@ jobs:
       # system-tests requires an API_KEY, but it does not have to be a valid key, as long as we don't run a scenario
       # that make assertion on backend data. Using a fake key allow to run system tests on PR originating from forks.
       # If ever it's needed, a valid key exists in the repo, using ${{ secrets.DD_API_KEY }}
-      DD_API_KEY: 1234567890abcdef1234567890abcdef
+      DD_API_KEY: ${{ secrets.FAKE_DD_API_KEY }}
       CMAKE_BUILD_PARALLEL_LEVEL: 12
       SYSTEM_TESTS_AWS_ACCESS_KEY_ID: ${{ secrets.IDM_AWS_ACCESS_KEY_ID }}
       SYSTEM_TESTS_AWS_SECRET_ACCESS_KEY: ${{ secrets.IDM_AWS_SECRET_ACCESS_KEY }}