enable git allrefs by default (nix-2.3 behavior)

nix_fetchGit.patch

diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc
index 9cbd39247..13f6e5b88 100644
--- a/src/libfetchers/git.cc
+++ b/src/libfetchers/git.cc
@@ -397,7 +397,7 @@ struct GitInputScheme : InputScheme
 
         bool shallow = maybeGetBoolAttr(input.attrs, "shallow").value_or(false);
         bool submodules = maybeGetBoolAttr(input.attrs, "submodules").value_or(false);
-        bool allRefs = maybeGetBoolAttr(input.attrs, "allRefs").value_or(false);
+        bool allRefs = maybeGetBoolAttr(input.attrs, "allRefs").value_or(true);
 
         std::string cacheType = "git";
         if (shallow) cacheType += "-shallow";