CI: Remove Ubuntu 20.04 (EOL May 31st) (#5849)

* ubuntu 20.04 eol

* Update release_template.md

* [skip ci] Delete .ci/Ubuntu20.04 directory

.ci/Ubuntu20.04/Dockerfile

@@ -1,26 +0,0 @@
-FROM ubuntu:20.04
-
-RUN apt-get update && \
-    DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
-        build-essential \
-        ccache \
-        clang-format \
-        cmake \
-        file \
-        g++ \
-        git \
-        liblzma-dev \
-        libmariadb-dev-compat \
-        libprotobuf-dev \
-        libqt5multimedia5-plugins \
-        libqt5sql5-mysql \
-        libqt5svg5-dev \
-        libqt5websockets5-dev \
-        protobuf-compiler \
-        qt5-default \
-        qt5-image-formats-plugins \
-        qtmultimedia5-dev \
-        qttools5-dev \
-        qttools5-dev-tools \
-    && apt-get clean \
-    && rm -rf /var/lib/apt/lists/*

.ci/release_template.md

@@ -20,7 +20,6 @@ Available pre-compiled binaries for installation:
   <b>Linux</b>
    • <kbd>Ubuntu 24.04 LTS</kbd> <sub><i>Noble Numbat</i></sub>
    • <kbd>Ubuntu 22.04 LTS</kbd> <sub><i>Jammy Jellyfish</i></sub>
-   • <kbd>Ubuntu 20.04 LTS</kbd> <sub><i>Focal Fossa</i></sub>
    • <kbd>Debian 12</kbd> <sub><i>Bookworm</i></sub>
    • <kbd>Debian 11</kbd> <sub><i>Bullseye</i></sub>
    • <kbd>Fedora 42</kbd>

.github/workflows/desktop-build.yml

@@ -110,11 +110,6 @@ jobs:
             version: 42
             package: RPM
 
-          - distro: Ubuntu
-            version: 20.04
-            package: DEB
-            test: skip    # Ubuntu 20.04 has a broken Qt for debug builds
-
           - distro: Ubuntu
             version: 22.04
             package: DEB