Reapply "Hotfix for Julia 1.10 claiming that istrans is type unstable"

This reverts commit 67bb055.

Author: penelopeysm

src/abstract_varinfo.jl

@@ -481,7 +481,15 @@ If `vns` is provided, then only check if this/these varname(s) are transformed.
 """
 istrans(vi::AbstractVarInfo) = istrans(vi, collect(keys(vi)))
 function istrans(vi::AbstractVarInfo, vns::AbstractVector)
-    return !isempty(vns) && all(Base.Fix1(istrans, vi), vns)
+    # This used to be: `!isempty(vns) && all(Base.Fix1(istrans, vi), vns)`.
+    # In theory that should work perfectly fine. For unbeknownst reasons,
+    # Julia 1.10 fails to infer its return type correctly. Thus we use this
+    # slightly longer definition.
+    isempty(vns) && return false
+    for vn in vns
+        istrans(vi, vn) || return false
+    end
+    return true
 end
 
 """