[Ubuntu] put Microsoft repo higher for dotnet (#6084)

images/linux/scripts/installers/dotnetcore-sdk.sh

@@ -16,6 +16,19 @@ DOTNET_TOOLS=$(get_toolset_value '.dotnet.tools[].name')
 # Disable telemetry
 export DOTNET_CLI_TELEMETRY_OPTOUT=1
 
+# There is a versions conflict, that leads to
+# Microsoft <-> Canonical repos dependencies mix up.
+# Give Microsoft's repo higher priority to avoid collisions.
+# See: https://github.com/dotnet/core/issues/7699
+
+cat << EOF > /etc/apt/preferences.d/dotnet
+Package: *net*
+Pin: origin packages.microsoft.com
+Pin-Priority: 1001
+EOF
+
+apt-get update
+
 for latest_package in ${LATEST_DOTNET_PACKAGES[@]}; do
     echo "Determing if .NET Core ($latest_package) is installed"
     if ! IsPackageInstalled $latest_package; then
@@ -26,6 +39,10 @@ for latest_package in ${LATEST_DOTNET_PACKAGES[@]}; do
     fi
 done
 
+rm /etc/apt/preferences.d/dotnet
+
+apt-get update
+
 # Get list of all released SDKs from channels which are not end-of-life or preview
 sdks=()
 for version in ${DOTNET_VERSIONS[@]}; do