When rebuilding emacs:

SUMMARY OF TEST RESULTS
-----------------------
Files examined: 267
Ran 3883 tests, 3832 results as expected, 1 unexpected, 50 skipped
1 files contained unexpected results:
  lisp/net/tramp-archive-tests.log
make[4]: *** [Makefile:320: check-doit] Error 1
make[4]: Leaving directory '/home/vlefevre/tmp/emacs-27.1+1/debian/build-lucid/test'
make[3]: *** [Makefile:289: check] Error 2
make[3]: Leaving directory '/home/vlefevre/tmp/emacs-27.1+1/debian/build-lucid/test'
make[2]: *** [Makefile:960: check] Error 2
make[2]: Leaving directory '/home/vlefevre/tmp/emacs-27.1+1/debian/build-lucid'
make[1]: *** [debian/rules:341: override_dh_auto_test] Error 2
make[1]: Leaving directory '/home/vlefevre/tmp/emacs-27.1+1'
make: *** [debian/rules:204: build] Error 2
dpkg-buildpackage: error: debian/rules build subprocess returned exit status 2
debuild: fatal error at line 1182:
dpkg-buildpackage -us -uc -ui -i -b failed

The failed test in lisp/net/tramp-archive-tests.log:

Test tramp-archive-test02-file-name-dissect condition:
    (ert-test-failed
     ((should
       (string-equal host
                     (url-hexify-string ...)))
      :form
      (string-equal "file%3A%2F%2F%2Fhome%2Fvlefevre%2Ftmp%2Femacs-27.1%252B1%2Fdebian%2Fbuild-src%2Ftest%2Flisp%2Fnet%2Ftramp-archive-resources%2Ffoo.tar.gz" "file%3A%2F%2F%2Fhome%2Fvlefevre%2Ftmp%2Femacs-27.1%2B1%2Fdebian%2Fbuild-src%2Ftest%2Flisp%2Fnet%2Ftramp-archive-resources%2Ffoo.tar.gz")
      :value nil))
   FAILED  3/8  tramp-archive-test02-file-name-dissect (0.031675 sec)

emacs FTBFS bugs seem to be already fixed in sid.

Thanks,
--
Tatsuya Kinoshita

According to an earlier message in the bug log this was fixed by version
1:28.2+1-6 in 2022.