fixup: alloy container.py — bump dagger build image to golang:alpine3.23

CI run 522 dagger job failed with `go.mod requires go >= 1.26.2 (running
go 1.25.9; GOTOOLCHAIN=local)`. golang:1.25-alpine3.22 was a holdover
from the original Dockerfile; alloy v1.16.0's go.mod requires Go 1.26.

Switching to golang:alpine3.23 (currently Go 1.26.2) — matches both
alloy's toolchain requirement and the go_build helper's image choice.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

containers/alloy/container.py

@@ -9,7 +9,8 @@ Notes:
   - promtail_journal_enabled is intentionally omitted: it requires
     libsystemd-dev and our k8s deployments read pod logs from the filesystem,
     not journald.
-  - Pinned to golang:1.25-alpine3.22 (matches upstream's tested Go toolchain).
+  - Uses golang:alpine3.23 (currently Go 1.26.2 — matches alloy v1.16.0's
+    go.mod toolchain requirement and the go_build helper's image choice).
 """
 
 import dagger
@@ -38,7 +39,7 @@ async def build(src: dagger.Directory) -> dagger.Container:
     # Stage 2: Build alloy via the upstream Makefile with embedded UI assets.
     builder = (
         dag.container()
-        .from_("golang:1.25-alpine3.22")
+        .from_("golang:alpine3.23")
         .with_exec(["apk", "add", "--no-cache", "build-base", "git", "make"])
         .with_directory("/app", source)
         .with_directory(