chore: unassume account credentials after ios test

Signed-off-by: Kevin Shan <[email protected]>

Author: Siqi-Shan

.codebuild/run_ios_modelgen_e2e_test.yml

@@ -23,6 +23,7 @@ phases:
       - cd $CODEBUILD_SRC_DIR && ./.codebuild/scripts/run-ios-modelgen-e2e-test.sh
   post_build:
     commands:
+      - source ./shared-scripts.sh && _unassumeTestAccountCredentials
       - aws sts get-caller-identity
       - source ./shared-scripts.sh && _scanArtifacts