gitcommit: fully implement warn_about_trailing_whitespace

Fixes #1761

ale_linters/gitcommit/gitlint.vim

@@ -23,8 +23,10 @@ function! ale_linters#gitcommit#gitlint#Handle(buffer, lines) abort
     for l:match in ale#util#GetMatches(a:lines, l:pattern)
         let l:code = l:match[2]
 
-        if l:code is# 'T2' && !ale#Var(a:buffer, 'warn_about_trailing_whitespace')
-            continue
+        if !ale#Var(a:buffer, 'warn_about_trailing_whitespace')
+            if l:code is# 'T2' || l:code is# 'B2'
+                continue
+            endif
         endif
 
         let l:item = {