chore(bootstrap-vue): Use our env variable to determine VUE version

Using our env variable in jest/CI to determine whether vue@2 or vue@3 is
used.

.gitlab-ci.yml

@@ -312,9 +312,7 @@ bootstrap-vue:
     - yarn run test
 
 bootstrap-vue_vue3:
-  extends: [bootstrap-vue]
-  variables:
-    USE_VUE3: '1'
+  extends: [bootstrap-vue, .use_vue3]
 
 .unit_tests:
   extends: [.node, .yarn_install]

src/vendor/bootstrap-vue/jest.config.js

-const useVue3 = 'USE_VUE3' in process.env
+const { USE_VUE_3 } = require('../../../use_vue3')
 
-const moduleNameMapper = useVue3
+const moduleNameMapper = USE_VUE_3
   ? {
       '^vue$': '@vue/compat',
       '^@vue/test-utils$': '@vue/test-utils-vue3'
@@ -15,7 +15,7 @@ module.exports = {
     '^.+\\.js$': 'babel-jest'
   },
   transformIgnorePatterns: ['/node_modules(?![\\\\/]vue-test-utils-compat[\\\\/])'],
-  coverageDirectory: useVue3 ? './coverage-vue3' : './coverage/',
+  coverageDirectory: USE_VUE_3 ? './coverage-vue3' : './coverage/',
   testEnvironmentOptions: {
     pretendToBeVisual: true
   },