Upgrade Simple Git to latest major and minor. (#1131)

This PR upgrades the version of `simple-git` used by the Theme. This will address a number of Snyk issues. In the latest version of `simple-git`, you import `simple-git` directly, not `simple-git/promise`. 

TEST=manual

Ensured that the logic for determining if the Theme is a submodule still worked as expected. This is the only usage of `simple-git` in the Theme.

package.json

@@ -54,7 +54,7 @@
     "postcss": "^8.4.14",
     "puppeteer": "^10.2.0",
     "serve": "^11.3.2",
-    "simple-git": "^2.24.0",
+    "simple-git": "^3.17.0",
     "testcafe": "^1.20.0",
     "underscore.string": "^3.3.6",
     "urijs": "^1.19.11",

postupgrade/utils.js

@@ -1,6 +1,6 @@
 const fs = require('fs');
 const path = require('path');
-const simpleGit = require('simple-git/promise')();
+const simpleGit = require('simple-git')();
 
 /**
  * Gets the value of a given --jambo command line argument.

static/package.json

@@ -40,7 +40,7 @@
     "rtlcss-webpack-plugin": "^4.0.7",
     "sass": "^1.34.0",
     "sass-loader": "^8.0.2",
-    "simple-git": "^2.15.0",
+    "simple-git": "^3.17.0",
     "webpack": "^5.37.1",
     "webpack-cli": "^4.2.0",
     "webpack-merge": "^5.7.3"