Update dependency go to 1.26

Author: gardener-ci-robot

.github/workflows/build.yaml

@@ -53,7 +53,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v5
         with:
-          go-version: '1.24'
+          go-version: '1.26'
       - uses: gardener/cc-utils/.github/actions/trusted-checkout@master
       - name: run-test-unit
         shell: bash
@@ -83,7 +83,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v5
         with:
-          go-version: '1.24'
+          go-version: '1.26'
       - uses: gardener/cc-utils/.github/actions/trusted-checkout@master
       - name: run-check
         run: |