ci(downgrade): allow-reresolve false (strict SciML default)

Use the strict SciML default `allow-reresolve: false` so Pkg.test must
instantiate the exact deps-floor + latest-transitive set with no
reconciliation. Verified locally on Julia 1.10 (deps-mode: only [deps]
[compat] pinned to floors, allow_reresolve=false):
  Quality Assurance: 10/10
  Basic Tests: 329 pass, 1 broken (pre-existing @test_broken), 330 total
  "Testing ExponentialUtilities tests passed" (exit 0)
No floor raises needed — current [deps] floors are strict-consistent with
the latest transitive ecosystem.

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

@@ -22,5 +22,5 @@ jobs:
       julia-version: "1.10"
       group: "${{ matrix.group }}"
       skip: "Pkg,TOML"
-      allow-reresolve: true
+      allow-reresolve: false
     secrets: "inherit"