Drop allow-reresolve input from downgrade workflow

The reusable SciML/.github downgrade workflows now always use
allow_reresolve: false and no longer accept an allow-reresolve input
(see SciML/.github#71). Remove the now-invalid input so this caller keeps
working once @v1 is retagged.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

.github/workflows/downgrade.yml

@@ -26,5 +26,4 @@ jobs:
       group: "${{ matrix.group }}"
       julia-version: "1.10"
       skip: "Pkg,TOML"
-      allow-reresolve: false
     secrets: "inherit"