Add CHANGELOG entry for 8.12.6
Add CHANGELOG entry for 8.12.6

t-zuehlsdorff/gitlabhq,daiyu/gitlab-zh,stoplightio/gitlabhq,dreampet/gitlab,LUMC/gitlabhq,mmkassem/gitlabhq,t-zuehlsdorff/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,htve/GitlabForChinese,daiyu/gitlab-zh,axilleas/gitlabhq,shinexiao/gitlabhq,dreampet/gitlab,iiet/iiet-git,darkrasid/gitlabhq,screenpages/gitlabhq,htve/GitlabForChinese,stoplightio/gitlabhq,shinexiao/gitlabhq,screenpages/gitlabhq,darkrasid/gitlabhq,dplarson/gitlabhq,dplarson/gitlabhq,iiet/iiet-git,dplarson/gitlabhq,dreampet/gitlab,LUMC/gitlabhq,axilleas/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,darkrasid/gitlabhq,t-zuehlsdorff/gitlabhq,shinexiao/gitlabhq,daiyu/gitlab-zh,openwide-java/gitlabhq,jirutka/gitlabhq,dplarson/gitlabhq,openwide-java/gitlabhq,t-zuehlsdorff/gitlabhq,htve/GitlabForChinese,screenpages/gitlabhq,jirutka/gitlabhq,LUMC/gitlabhq,stoplightio/gitlabhq,axilleas/gitlabhq,openwide-java/gitlabhq,shinexiao/gitlabhq,openwide-java/gitlabhq,iiet/iiet-git,daiyu/gitlab-zh,dreampet/gitlab,mmkassem/gitlabhq,darkrasid/gitlabhq,LUMC/gitlabhq,screenpages/gitlabhq,stoplightio/gitlabhq,axilleas/gitlabhq,htve/GitlabForChinese