upgrade: RELEASE_NUMBERS is a variable with all known releases

the development branch is not build for v1.21 & v1.20 because they
pre-date the hard fork and near EOL

forgejo/build.sh

@@ -12,18 +12,22 @@ DIR=$2
 v=$(echo $version | sed -E -e 's/^([0-9]+\.[0-9]+).*/\1/')
 read url ref semver < $SELF_DIR/sources/$v
 
-rm -fr $DIR/src
-if [[ "$ref" =~ ^refs/ ]] ; then
-    git clone --depth 1 $url $DIR/src
+if ! test -d $DIR/src ; then
+    mkdir -p $DIR/src
     cd $DIR/src
-    git fetch origin +$ref:$ref
-    git checkout -b $v $ref
+    git init
+    git remote add origin $url
 else
-    git clone --depth 1 -b $ref $url $DIR/src
     cd $DIR/src
 fi
 
+if ! [[ "$ref" =~ ^refs/ ]] ; then
+    ref=refs/heads/$ref
+fi
+git fetch --update-head-ok origin +$ref:$ref
+git switch --force-create $v $ref
+
 export TAGS="bindata sqlite sqlite_unlock_notify" FORGEJO_VERSION=$semver
 make deps-backend backend
 make generate forgejo
-mv forgejo $DIR/forgejo-$version
+cp -a forgejo $DIR/forgejo-$v-dev