ci: fix #2

Author: ajay

tools/deps/os/ubuntu.sh

@@ -8,6 +8,7 @@ sudo apt -y install		\
 	python3				\
 	python3-pip
 
+sudo apt -y purge libc++* clang*
 wget --directory-prefix /tmp https://apt.llvm.org/llvm.sh
 chmod +x /tmp/llvm.sh
 sudo /tmp/llvm.sh 20
@@ -16,7 +17,6 @@ sudo apt -y install		\
 	clang-format-20		\
 	libclang-20-dev		\
 	llvm-20-dev
-sudo apt -y purge libc++*
 
 wget --directory-prefix /tmp https://launchpad.net/ubuntu/+archive/primary/+files/iwyu_8.23-1_amd64.deb
 sudo dpkg -i /tmp/iwyu_8.23-1_amd64.deb