chore(deps): update dependency go to v1.26.2

Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

go.mod

@@ -2,7 +2,7 @@ module github.com/nginx/agent/v3
 
 go 1.25.0
 
-toolchain go1.25.8
+toolchain go1.26.2
 
 require (
 	buf.build/gen/go/bufbuild/protovalidate/protocolbuffers/go v1.36.9-20250912141014-52f32327d4b0.1