CI: Expand explanation of allow_failure

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index f79c3a79d08975d874b011a377f4f9820e43b320..9ef8b3591d6a1c07ff6e4e9fcc7748afa557aadc 100644 (file)
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -60,6 +60,11 @@ test-rust-upstream:
 
 # This test is marked allow-fail because Debian development breaks
 # things on a regular basis.
+# Specifically, it can be impossible (or at least very inconvenient)
+# to make code that works both before and after some dependency crate
+# version transition.
+# If multiple such transitions are occurring at once, both unstable
+# and testing might be broken, halfway through our response.
 test-debian-trixie:
   stage: test
   image: "debian:trixie-slim"
@@ -71,7 +76,7 @@ test-debian-trixie:
     - dpkg-buildpackage -uc -b
 
 # This test is marked allow-fail because Debian development breaks
-# things on a regular basis.
+# things on a regular basis.  See also, above.
 test-debian-unstable:
   stage: test
   image: "debian:unstable-slim"