[ubuntu] Document GHC apt repository (#3268)

images/linux/scripts/SoftwareReport/SoftwareReport.Common.psm1

@@ -251,7 +251,8 @@ function Build-PHPTable {
 function Get-GHCVersion {
     $(ghc --version) -match "version (?<version>\d+\.\d+\.\d+)" | Out-Null
     $ghcVersion = $Matches.version
-    return "GHC $ghcVersion"
+    $aptSourceRepo = Get-AptSourceRepository -PackageName "ghc"
+    return "GHC $ghcVersion (apt source repository: $aptSourceRepo)"
 }
 
 function Get-GHCupVersion {

images/linux/scripts/installers/haskell.sh

@@ -49,4 +49,8 @@ ln -s "/opt/ghc/$defaultGHCVersion/bin/ghc" "/usr/bin/ghc"
 # Install the latest stable release of haskell stack
 curl -sSL https://get.haskellstack.org/ | sh
 
+# remove PPA repo
+echo "ghc ppa:hvr/ghc" >> $HELPER_SCRIPTS/apt-sources.txt
+add-apt-repository --remove ppa:hvr/ghc
+
 invoke_tests "Haskell"