chore(deps): update ubuntu docker tag to groovy-20210723

Author: renovate[bot]

Dockerfile

@@ -1,15 +1,15 @@
 FROM snapcore/snapcraft AS snapcraft
 # Using multi-stage dockerfile to obtain snapcraft binary
 
-FROM ubuntu:groovy AS flutterbuilder
+FROM ubuntu:groovy-20210723 AS flutterbuilder
 RUN apt-get update \
     && apt-get install -y \
         git curl unzip
 # Install Flutter from the beta channel
 RUN git clone --single-branch --depth=1 --branch beta https://github.com/flutter/flutter /opt/flutter 2>&1 \
     && /opt/flutter/bin/flutter doctor -v
 
-FROM ubuntu:groovy AS xarbuilder
+FROM ubuntu:groovy-20210723 AS xarbuilder
 RUN apt-get update \
 	&& apt-get install -y \
 		git libssl-dev libxml2-dev make g++ autoconf zlib1g-dev
@@ -22,7 +22,7 @@ RUN git clone --single-branch --depth=1 --branch xar-1.6.1 https://github.com/ma
 	&& make 2>&1 \
 	&& make install 2>&1
 
-FROM ubuntu:groovy AS bomutilsbuilder
+FROM ubuntu:groovy-20210723 AS bomutilsbuilder
 RUN apt-get update \
 	&& apt-get install -y \
 	    git make g++
@@ -32,7 +32,7 @@ RUN git clone --single-branch --depth=1 --branch 0.2 https://github.com/hogliux/
 	&& make install 2>&1
 
 # Fixed using https://github.com/AppImage/AppImageKit/issues/828
-FROM ubuntu:groovy as appimagebuilder
+FROM ubuntu:groovy-20210723 as appimagebuilder
 RUN apt-get update \
 	&& apt-get install -y \
 	    curl
@@ -44,7 +44,7 @@ RUN cd /opt \
 	&& mv squashfs-root appimagetool
 
 # groovy ships with a too old meson version
-FROM ubuntu:groovy AS pacmanbuilder
+FROM ubuntu:groovy-20210723 AS pacmanbuilder
 ENV DEBIAN_FRONTEND=noninteractive
 RUN apt-get update \
     && apt-get install -y \