[PATCH] ci: container: downgrade LLVM to v20

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

It's currently not possible to build LLVM v21 in our Trixie container:

  Some packages could not be installed. This may mean that you have
  requested an impossible situation or if you are using the unstable
  distribution that some required packages have not yet been created
  or been moved out of Incoming.
  The following information may help to resolve the situation:

  The following packages have unmet dependencies:
   clang-21 : Depends: libstdc++-15-dev but it is not installable
              Depends: libgcc-15-dev but it is not installable
              Depends: libobjc-15-dev but it is not installable
              Recommends: llvm-21-dev but it is not going to be installed
              Recommends: clang-tools-21 but it is not going to be installed
   libllvm21 : Depends: libxml2-16 (>= 2.14.1) but it is not installable
   lldb-21 : Depends: liblldb-21 but it is not going to be installed
             Depends: libxml2-16 (>= 2.14.1) but it is not installable
             Depends: python3-lldb-21 but it is not going to be installed
  E: Unable to correct problems, you have held broken packages.
  E: The following information from --solver 3.0 may provide additional context:
     Unable to satisfy dependencies. Reached two conflicting decisions:
     1. lldb-21:amd64=1:21.1.4~++20251021083224+222fc11f2b8f-1~exp1~20251021083341.56 is selected for install
     2. lldb-21:amd64 Depends libxml2-16 (>= 2.14.1)
        but none of the choices are installable:
        [no choices]

Until resolved, downgrade to LLVM v20. We currently need this only for
libfuzzer.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 test/Containerfile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/Containerfile b/test/Containerfile
index 2c0a20ec59da..6b4a97147c2e 100644
--- a/test/Containerfile
+++ b/test/Containerfile
@@ -62,7 +62,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 	&& rm -rf /var/lib/apt/lists/*
 
 ENV GCC_VERSION=15.2.0
-ENV LLVM_VERSION=21
+ENV LLVM_VERSION=20
 
 RUN apt-get update && apt-get install -y --no-install-recommends lsb-release gnupg \
 	&& wget https://apt.llvm.org/llvm.sh \
-- 
2.47.3