Installing clang ubuntu docker

Hi folks, I’m trying to create a docker image with clang 13 to compile CPython, but I keep getting the following error

Step 6/9 : RUN add-apt-repository " llvm-toolchain-focal-13 main"
 ---> Running in 401353b306da
Hit:2 focal-security InRelease
Hit:3 focal InRelease
Hit:4 focal-updates InRelease
Hit:5 focal-backports InRelease
Ign:1 focal InRelease
Err:6 focal Release
  404  Not Found [IP: 443]
Reading package lists...
E: The repository ' focal Release' does not have a Release file.
The command '/bin/sh -c add-apt-repository " llvm-toolchain-focal-13 main"' returned a non-zero code: 100

Here’s my dockerfile

FROM ubuntu:focal

WORKDIR /opt/cpython-3.9

RUN apt-get update
RUN apt-get install --yes wget gnupg2 software-properties-common

RUN wget -O -| apt-key add -
RUN add-apt-repository " llvm-toolchain-focal-13 main"

RUN apt-get update && apt-get upgrade
RUN apt-get install --yes clang-13 lld-13 libncurses-dev libgdbm-dev libz-dev tk-dev libsqlite3-dev libreadline-dev liblzma-dev libffi-dev libssl-dev

RUN apt-get update -qq \
    && apt-get install --yes build-essential curl \
    curl -fsSL \
    | tar xz --strip-components 1 \
    && CC=clang ./configure --with-lto=full --enable-shared --enable-optimizations --prefix /usr/local/cpython-3.9 \
    && make \
    && make install

Am I missing something? Thanks in advance!