build-env.sh: bump dt-schema to 2026.06

Bump DT schema up to 2026.06

Signed-off-by: Nishanth Menon <nm@ti.com>

Author: nmenon

build-env.sh

@@ -14,7 +14,7 @@ export SPARSE_TAG=master
 # https://repo.or.cz/smatch.git
 export SMATCH_TAG=master
 # https://github.com/devicetree-org/dt-schema/tags
-export DTSCHEMA_REV=v2026.04
+export DTSCHEMA_REV=v2026.06
 # https://github.com/masoncl/review-prompts
 export REVIEW_PROMPTS=main
 # https://github.com/facebookexperimental/semcode