devcontainer: fix package manager command to install git and bash in …

…alpine image with 'apk' instead of 'apt'

.devcontainer/slackbot/Dockerfile

@@ -3,6 +3,6 @@ FROM node:20-alpine
 # Install build dependencies for node-canvas
 # https://github.com/Automattic/node-canvas/issues/2239#issuecomment-2005970772
 RUN apk update && apk add build-base g++ cairo-dev pango-dev giflib-dev && \
-    apt add git bash
+    apk add git bash
 
 WORKDIR /code