ci: build with Go 1.26

staticcheck and govulncheck at latest require Go 1.26.0 or newer.
The runner used Go 1.25, so both tools failed to install.

.github/workflows/pr.yaml

@@ -18,7 +18,7 @@ jobs:
   pr-checks:
     uses: lukaszraczylo/shared-actions/.github/workflows/go-pr.yaml@main
     with:
-      go-version: "1.25.x"
+      go-version: "1.26.x"
       coverage-threshold: 75
     secrets: inherit
 
@@ -40,7 +40,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v6
         with:
-          go-version: "1.25.x"
+          go-version: "1.26.x"
           cache: true
 
       - name: yaegi-check