ci: instal python3 in ubuntu docker images

Author: variar

docker/ubuntu20.04/Dockerfile

@@ -3,7 +3,7 @@ FROM ubuntu:focal
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update -y && \
-    apt-get install --no-install-recommends build-essential \
+    apt-get install --no-install-recommends build-essential python3 python-is-python3 \
                     qtbase5-dev qt5-qmake qtbase5-dev-tools qttools5-dev qttranslations5-l10n\
                     libboost-dev libssl-dev libicu-dev libcurl4-openssl-dev \
                     ragel ninja-build zlib1g-dev git pkg-config \

docker/ubuntu20.04_qt5.15/Dockerfile

@@ -6,7 +6,7 @@ RUN apt-get update -y && \
     apt-get install --no-install-recommends software-properties-common -y && \
     add-apt-repository ppa:beineri/opt-qt-5.15.3-focal -y && \
     apt-get update -y && \
-    apt-get install --no-install-recommends build-essential \
+    apt-get install --no-install-recommends build-essential python3 python-is-python3 \
                     qt515base qt515svg qt515tools qt515imageformats qt515translations \
                     mesa-common-dev libglu1-mesa-dev \
                     libboost-dev libicu-dev libssl-dev libcurl4-openssl-dev \

docker/ubuntu22.04/Dockerfile

@@ -3,7 +3,7 @@ FROM ubuntu:jammy
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt update -y && \
-    apt install --no-install-recommends build-essential \
+    apt install --no-install-recommends build-essential python3 python-is-python3 \
                     qtbase5-dev qt5-qmake qtbase5-dev-tools qttools5-dev qttranslations5-l10n \
                     libboost-dev libssl-dev libcurl4-openssl-dev \
                     ragel ninja-build zlib1g-dev git pkg-config \

docker/ubuntu24.04/Dockerfile

@@ -3,7 +3,7 @@ FROM ubuntu:noble
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN apt-get update -y && \
-    apt-get install --no-install-recommends build-essential \
+    apt-get install --no-install-recommends build-essential python3 python-is-python3 \
                     qt6-base-dev qt6-5compat-dev qt6-translations-l10n \
                     qt6-tools-dev-tools qt6-base-dev-tools qt6-tools-dev \
                     libboost-dev libicu-dev libssl-dev libcurl4-openssl-dev \