ci: drop Dependabot, which cannot clone this repo

Both first runs on 2026-10-31 failed with Dependabot::OutOfDisk after
34 minutes. Dependabot clones with --recurse-submodules, and TechEngine
carries TechAPI as its own submodule, so the clone loops until the disk
is full; dependabot.yml has no setting that stops the recursion. The
TechEngine pin and the pinned action SHAs are bumped by hand instead.

Refs #297

Author: Seungpyo1007

.github/dependabot.yml

@@ -77,8 +77,10 @@ This repo follows git-flow:
 | `feat/*`, `data/*`, `fix/*`, `chore/*` | Short-lived work branches, cut from `develop`. |
 
 A release is a PR from `develop` to `main`; merging it deploys the site.
-Dependabot opens the TechEngine submodule bump (weekly) and GitHub Actions
-updates (monthly) as PRs into `develop`; they are merged by hand like any other.
+The TechEngine pin and the pinned action SHAs are bumped by hand, in a PR into
+`develop` that pr-checks validates like any other. Dependabot can't do it:
+TechEngine carries TechAPI as its own submodule, and Dependabot's recursive
+clone runs out of disk on that loop.
 
 ## Contributing