chore(dev): upgrade godevcontainer to v0.21

See [release notes](https://github.com/qdm12/godevcontainer/releases/tag/v0.21.0)

Notably:
- Go upgraded from 1.23 to 1.25
- golangci-lint upgraded to v2.4.0
- Alpine upgraded from 3.20 to 3.22
- Disable package comment requirement by gopls' staticcheck
- Pull container image from ghcr.io

.devcontainer/Dockerfile

@@ -1 +1 @@
-FROM qmcgaw/godevcontainer:v0.20-alpine
+FROM qmcgaw/godevcontainer:v0.21-alpine

.devcontainer/devcontainer.json

@@ -100,6 +100,9 @@
                     "formatting.gofumpt": true,
                     "usePlaceholders": false,
                     "staticcheck": true,
+                    "ui.diagnostic.analyses": {
+                        "ST1000": false
+                    },
                     "vulncheck": "Imports"
                 },
                 "remote.extensionKind": {