Downgrade Flatcar version from 4081.0.0 to 3815.2.2

Makefile.versions

@@ -1,5 +1,10 @@
 E2ETEST_K8S_VERSION  := 1.30.0
 # ref to https://github.com/orgs/flatcar/packages/container/package/flatcar-sdk-amd64
-FLATCAR_VERSION := 4081.0.0
+# In the container image of flatcar 4081.0.0,
+# the method for determining capabilities in perf (version 6.7) has changed.
+# As a result, we cannot obtain profiling with perf unless the value of kptr_restrict is set to 0.
+# The capability determination method has been improved in perf version 6.12.
+# Until the version of perf included in the flatcar image is upgraded to 6.12, we will keep the flatcar version at 3815.2.2(perf version 6.3).
+FLATCAR_VERSION := 3815.2.2
 KIND_VERSION := 0.25.0
 KUSTOMIZE_VERSION := 5.5.0