llvm: Downgrade to 20.0.x release world

Signed-off-by: Nishanth Menon <nm@ti.com>

Author: nmenon

llvm-config/etc/apt/sources.list.d/llvm.list

@@ -1,2 +1,2 @@
-deb [signed-by=/etc/apt/trusted.gpg.d/apt.llvm.org.asc] http://apt.llvm.org/trixie/ llvm-toolchain-trixie main
-deb-src [signed-by=/etc/apt/trusted.gpg.d/apt.llvm.org.asc] http://apt.llvm.org/trixie/ llvm-toolchain-trixie main
+deb [signed-by=/etc/apt/trusted.gpg.d/apt.llvm.org.asc] http://apt.llvm.org/trixie/ llvm-toolchain-trixie-20 main
+deb-src [signed-by=/etc/apt/trusted.gpg.d/apt.llvm.org.asc] http://apt.llvm.org/trixie/ llvm-toolchain-trixie-20 main