build: move pact dependency to devDependencies (#823)

Pact is a testing library. It is not used in to run the
Learning MFE application. Therefore, it belongs in the
devDependencies section of package.json, not the
dependencies section.

package.json

@@ -43,7 +43,6 @@
     "@fortawesome/free-regular-svg-icons": "5.15.4",
     "@fortawesome/free-solid-svg-icons": "5.15.4",
     "@fortawesome/react-fontawesome": "0.1.16",
-    "@pact-foundation/pact": "9.17.0",
     "@popperjs/core": "2.10.2",
     "@reduxjs/toolkit": "1.6.2",
     "classnames": "2.3.1",
@@ -68,6 +67,7 @@
   },
   "devDependencies": {
     "@edx/frontend-build": "9.0.6",
+    "@pact-foundation/pact": "9.17.0",
     "@testing-library/dom": "7.16.3",
     "@testing-library/jest-dom": "5.15.1",
     "@testing-library/react": "10.3.0",