build: clang-12 is not supported in jammy

.gitpod.Dockerfile

@@ -2,7 +2,6 @@ FROM trainiteu/gitpod-cpp
 
 # Add clang-12 and clang-15 apt repositories
 RUN lsb_rel=`lsb_release -cs` \
-  && sudo add-apt-repository "deb http://apt.llvm.org/${lsb_rel}/ llvm-toolchain-${lsb_rel}-12 main" \
   && sudo add-apt-repository "deb http://apt.llvm.org/${lsb_rel}/ llvm-toolchain-${lsb_rel}-13 main" \
   && sudo add-apt-repository "deb http://apt.llvm.org/${lsb_rel}/ llvm-toolchain-${lsb_rel}-14 main" \
   && sudo add-apt-repository "deb http://apt.llvm.org/${lsb_rel}/ llvm-toolchain-${lsb_rel} main"
@@ -11,6 +10,5 @@ RUN lsb_rel=`lsb_release -cs` \
 RUN sudo install-packages \
   g++-10 \
   g++-11 \
-  clang-12 \
   clang-13 \
   clang-14