chore: bump workflow tag to latest

Author: tstephen-nhs

.github/workflows/run_regression_tests.yml

@@ -63,7 +63,7 @@ jobs:
 
             # this should be the tag of the regression test workflow you want to run
             # This will normally be the same as REGRESSION_TEST_REPO_TAG
-            REGRESSION_TEST_WORKFLOW_TAG=aea-6055-post-dated-updates
+            REGRESSION_TEST_WORKFLOW_TAG=v3.9.26
 
             curl https://raw.githubusercontent.com/NHSDigital/electronic-prescription-service-api-regression-tests/refs/tags/${REGRESSION_TEST_WORKFLOW_TAG}/scripts/run_regression_tests.py -o run_regression_tests.py
             poetry install