chore: upgrade Go version in devcontainer image to 1.26 (#37374)

Upgrade the base devcontainer image to prevent the in-container
toolchain upgrade from breaking `make build`.

Solves #37373

Co-authored-by: Morgan PEYRE <morgan.peyre@brickcode.tech>

.devcontainer/devcontainer.json

@@ -1,6 +1,6 @@
 {
   "name": "Gitea DevContainer",
-  "image": "mcr.microsoft.com/devcontainers/go:1.25-trixie",
+  "image": "mcr.microsoft.com/devcontainers/go:1.26-trixie",
   "containerEnv": {
     // override "local" from packaged version
     "GOTOOLCHAIN": "auto"