Bump Python FnAPI beam-master container (#38041)

* Bump Python FnAPI beam-master container 

Candidate: beam-master-20260401-00

* Apply suggestion from @jrmccluskey

Co-authored-by: Jack McCluskey <34928439+jrmccluskey@users.noreply.github.com>

---------

Co-authored-by: Jack McCluskey <34928439+jrmccluskey@users.noreply.github.com>

Author: apanich

sdks/python/apache_beam/runners/dataflow/internal/names.py

@@ -35,6 +35,6 @@
 # Update this tag whenever there is a change that
 # requires changes to SDK harness container or SDK harness launcher.
 
-BEAM_DEV_SDK_CONTAINER_TAG = 'beam-master-20260316'
+BEAM_DEV_SDK_CONTAINER_TAG = 'beam-master-20260402'
 
 DATAFLOW_CONTAINER_IMAGE_REPOSITORY = 'gcr.io/cloud-dataflow/v1beta3'