build: add option to allow uploading dirty nightly builds

contrib/make_nightly_build

@@ -6,6 +6,7 @@ for arg in "$@"; do
     --no-github) NO_GITHUB=1 ;;
     --no-codeberg) NO_CODEBERG=1 ;;
     --no-flowcontrol) NO_FLOWCONTROL=1 ;;
+    --allow-dirty) ALLOW_DIRTY=1 ;;
     esac
 done
 
@@ -33,6 +34,7 @@ fi
 
 DIFF="$(git diff --stat --patch HEAD)"
 
+if [ -z "$ALLOW_DIRTY" ]; then
     if [ -n "$DIFF" ]; then
         echo there are outstanding changes:
         echo "$DIFF"
@@ -46,6 +48,7 @@ if [ -n "$UNPUSHED" ]; then
         echo "$UNPUSHED"
         exit 1
     fi
+fi
 
 # get latest version tag