docker_templates_amd64.yml: reduce the max_instances of
docker-amd64-tf-m-jammy-iar to 5

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: I4e9c664c75848d1e395b71a30245207d7c20ebac
diff --git a/docker_templates_amd64.yml b/docker_templates_amd64.yml
index b0bded8..3923691 100644
--- a/docker_templates_amd64.yml
+++ b/docker_templates_amd64.yml
@@ -35,7 +35,7 @@
   launch_method: 'launch_ssh'
   ssh: !include docker_ssh_buildslave.yml
   volumes: '/data/shared:/srv/shared:rw'
-  max_instances: '20'
+  max_instances: '5'
   environment_variables:
       - PATH : '/home/buildslave/tools/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin'
       - PLANTUML_JAR_PATH : '/usr/share/plantuml/plantuml.jar'