Updated Dockerfile to use golang:1.26 as base image (#148)

#### Type of change

- Improvement (improvement to code, performance, etc)

#### Description

The new `fabric-x-tools` require `go:1.26` to be built. This PR fixes
the issue for the image build.

Signed-off-by: pco <pasquale.convertini@ibm.com>

Author: pasquale95

Dockerfile

@@ -8,7 +8,7 @@
 ###########################################
 # Stage 1: Build image
 ###########################################
-FROM golang:1.25 AS builder
+FROM golang:1.26 AS builder
 
 # Build environment variables
 ENV CGO_ENABLED=1