QA: pin SciMLTesting compat floor to 1.7 (public-API EI gate)

The two public-API ExplicitImports checks
(check_all_qualified_accesses_are_public,
check_all_explicit_imports_are_public) are gated to Julia >= 1.11 only
from SciMLTesting 1.7.0. With the now-empty public-API ignore-lists in
qa.jl, the QA group relies on that gate so the LTS (1.10) does not
spuriously flag public-backported names. Raise the qa-env compat floor
from "1.6" to "1.7" so the resolved SciMLTesting always carries the gate.

Verified against registered releases (FVM dev'd via [sources], no dev of
base libs):
- Julia 1.12 (public-API checks RUN, no ignores): QA group 18/18 pass,
  0 fail/error/broken. Resolved SciMLBase 3.27.0, SciMLTesting 1.7.0,
  CommonSolve 0.2.9, ExplicitImports 1.15.0, JET 0.11.5, Aqua 0.8.16.
- Julia 1.10 lts (public-API checks skipped by the 1.7 gate): QA group
  16/16 pass, 0 fail/error/broken (the 2-test delta is exactly the two
  gated public-API checks).

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

Author: ChrisRackauckas

test/qa/Project.toml

@@ -13,6 +13,6 @@ FiniteVolumeMethod1D = {path = "../.."}
 Aqua = "0.8"
 JET = "0.9,0.10,0.11"
 SafeTestsets = "0.0.1, 0.1"
-SciMLTesting = "1.6"
+SciMLTesting = "1.7"
 Test = "1"
 julia = "1.10"