CurlApacheMirrorDownloadStrategy: ignore HOMEBREW_CURL_VERBOSE

Fixes Homebrew/homebrew#43002

Closes Homebrew/homebrew#43058.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/download_strategy.rb

@@ -359,6 +359,7 @@ class CurlApacheMirrorDownloadStrategy < CurlDownloadStrategy
     buf = ""
 
     pid = fork do
+      ENV.delete "HOMEBREW_CURL_VERBOSE"
       rd.close
       $stdout.reopen(wr)
       $stderr.reopen(wr)