MAINT: Pin highs to a version without scipygh-15888

MAINT: Switch to the scipy fork of highs

TST: xfail known flaky test

Co-authored-by: mckib2 <mckib2@users.noreply.github.com>

MAINT: Add a note on .gitmodule location

Co-authored-by: h-vetinari <h-vetinari@users.noreply.github.com>

.gitmodules

@@ -16,7 +16,8 @@
 [submodule "scipy/_lib/array_api_compat"]
 	path = scipy/_lib/array_api_compat
 	url = https://github.com/data-apis/array-api-compat.git
+# All submodules are required to be under subprojects for meson:
+# https://mesonbuild.com/Subprojects.html#why-must-all-subprojects-be-inside-a-single-directory
 [submodule "subprojects/highs"]
 	path = subprojects/highs
-	url = https://github.com/HaoZeke/highs
-	branch = forSciPy
+	url = https://github.com/scipy/highs

scipy/optimize/tests/test_milp.py

@@ -294,6 +294,8 @@ def test_infeasible_prob_16609():
 _msg_sol = "Serious numerical difficulties encountered. (HiGHS Status 16:"
 
 
+# See https://github.com/scipy/scipy/pull/19255#issuecomment-1778438888
+@pytest.mark.xfail(reason="Often buggy, revisit with callbacks, gh-19255")
 @pytest.mark.skipif(np.intp(0).itemsize < 8,
                     reason="Unhandled 32-bit GCC FP bug")
 @pytest.mark.parametrize(["options", "msg"], [({"time_limit": 0.1}, _msg_time),

subprojects/highs.wrap

@@ -1,3 +1,3 @@
 [wrap-git]
-url = https://github.com/HaoZeke/highs.git
-revision = 704a264a4123178ab09776864ba5bcbbdb69e3f7
+url = https://github.com/scipy/highs.git
+revision = a0df06fb20f2c67c02cf84d8a3b72862c2ab2b27