It's disappointing to see Emacs 26.3 fail to propagate to Debian testing for the best part of six months due to this issue. This "FTBS" is a single test failure on mips, in test set-process-filter-t. This test is not present prior to Emacs 26.3. It was added for https://debbugs.gnu.org/36591 , so if anyone is using Debian Emacs on mips, they could try investigating the test failure using the information in that report. Otherwise, skipping the test on mips would allow people on other platforms to get an updated Emacs.