Disable browserslist warning in CI jobs

browserslist throws a warning if certain dependencies are too old. As we
generally are not backporting browserslist updates, this can lead to
errors in CI. Previously we have caught the error in rake, but they have
changed the error message so it is failing again.

By simply setting the BROWSERSLIST_IGNORE_OLD_DATA env variable, we can
circumvent this issue.

.gitlab/ci/frontend.gitlab-ci.yml

@@ -15,6 +15,9 @@
   variables:
     SETUP_DB: "false"
     WEBPACK_VENDOR_DLL: "true"
+    # Disable warnings in browserslist which can break on backports
+    # https://github.com/browserslist/browserslist/blob/a287ec6/node.js#L367-L384
+    BROWSERSLIST_IGNORE_OLD_DATA: "true"
   stage: prepare
   script:
     - *yarn-install
@@ -164,6 +167,10 @@ graphql-schema-dump:
   extends:
     - .default-retry
     - .yarn-cache
+  variables:
+    # Disable warnings in browserslist which can break on backports
+    # https://github.com/browserslist/browserslist/blob/a287ec6/node.js#L367-L384
+    BROWSERSLIST_IGNORE_OLD_DATA: "true"
   stage: test
 
 eslint-as-if-foss:

.gitlab/ci/rails.gitlab-ci.yml

@@ -234,6 +234,9 @@ update-gitaly-binaries-cache:
   variables:
     SETUP_DB: "false"
     ENABLE_SPRING: "1"
+    # Disable warnings in browserslist which can break on backports
+    # https://github.com/browserslist/browserslist/blob/a287ec6/node.js#L367-L384
+    BROWSERSLIST_IGNORE_OLD_DATA: "true"
 
 update-static-analysis-cache:
   extends: