Fixed tests not running as expected for yarn test command

When executing tests via `yarn test` they are executed inside of a
container. The tests that are being executed are the ones added when the
container was first built. Subsequent changes to the tests are not causing
docker-compose to rebuild the container meaning the same set of tests were
always being executed. This change mounts the `src` directory into the
container so that the tests are always up to date.

docker-compose.testing.yml

@@ -1,6 +1,8 @@
 services:
-  activitypub:
+  activitypub-testing:
     build: .
+    volumes:
+      - ./src:/opt/activitypub/src
     environment:
       - MYSQL_USER=ghost
       - MYSQL_PASSWORD=password

package.json

@@ -13,7 +13,7 @@
     "test:integration": "c8 --src src --all --reporter text --reporter cobertura mocha -r tsx './src/**/*.integration.test.ts'",
     "test:code": "c8 --src src --all --reporter text --reporter cobertura mocha -r tsx './src/**/*.test.ts'",
     "test:all": "yarn test:types && yarn test:code",
-    "test": "docker compose -f docker-compose.testing.yml up --abort-on-container-exit --exit-code-from activitypub",
+    "test": "docker compose -f docker-compose.testing.yml up --abort-on-container-exit --exit-code-from activitypub-testing",
     "lint:code": "eslint *.js lib/ --ext .js --cache",
     "lint": "yarn lint:code"
   },