Update dependency go to 1.26 (#91)

Author: gardener-ci-robot

.github/workflows/build.yaml

@@ -46,7 +46,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v5
         with:
-          go-version: '1.23'
+          go-version: '1.26'
       - uses: gardener/cc-utils/.github/actions/trusted-checkout@master
       - name: verify
         run: |