ci: rename update-scripts → ci

This changes how we think about this directory; it does not need to be
exclusively for scripts related to updates, but should be a place for
any scripts intended to be run by CI workflows.

This mindset should make it easier to develop and test the business
logic of workflows, without always needing to test "in production" on
the nixvim repo or a fork.

.github/workflows/update.yml

@@ -132,7 +132,7 @@ jobs:
         id: update_flake_lock
         if: inputs.update_lock || github.event_name == 'schedule'
         run: |
-          nix-build ./update-scripts -A update
+          nix-build ./ci -A update
           ./result/bin/update --commit --github-output
 
       - name: Update generated files
@@ -140,7 +140,7 @@ jobs:
         if: inputs.generate || github.event_name == 'schedule'
         run: |
           old=$(git show --no-patch --format=%h)
-          nix-build ./update-scripts -A generate
+          nix-build ./ci -A generate
           ./result/bin/generate --commit
           new=$(git show --no-patch --format=%h)
           if [ "$old" != "$new" ]; then