dev-python/cython: suppress OpenMP parallelism in tests

We already pass MAKEOPTS parallelism to the testsuite's -j option. Some
of the tests also internally use OpenMP, and implicitly parallelize
according to nproc.

This consistently broke testing on the arm devbox, where nproc == 96,
even if using low -j values like "10":

```
libgomp: Thread creation failed: Resource temporarily unavailable
```

We can't get libgomp to subscribe to a jobserver. We don't even know if
e.g. steve is running, and cython itself doesn't use GNU Make (which
would make its own jobserver). But we can reasonably assume cython's
already-parallel testsuite will run as much parallelism as needed. We
don't need OpenMP-based over-parallelization, it will always just cause
harm. Disable it entirely.

Signed-off-by: Eli Schwartz <eschwartz@gentoo.org>

dev-python/cython/cython-3.1.7.ebuild

@@ -69,6 +69,10 @@ python_test() {
 	# Needed to avoid confusing cache tests
 	unset CYTHON_FORCE_REGEN
 
+	# uses $(nproc) to additionally parallelize many OpenMP-based jobs,
+	# leading to overcommitting
+	local -x OMP_NUM_THREADS=1
+
 	tc-export CC
 
 	local testargs=(

dev-python/cython/cython-3.1.8.ebuild

@@ -69,6 +69,10 @@ python_test() {
 	# Needed to avoid confusing cache tests
 	unset CYTHON_FORCE_REGEN
 
+	# uses $(nproc) to additionally parallelize many OpenMP-based jobs,
+	# leading to overcommitting
+	local -x OMP_NUM_THREADS=1
+
 	tc-export CC
 
 	local testargs=(

dev-python/cython/cython-3.2.3.ebuild

@@ -1,4 +1,4 @@
-# Copyright 1999-2025 Gentoo Authors
+# Copyright 1999-2026 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=8
@@ -69,6 +69,10 @@ python_test() {
 	# Needed to avoid confusing cache tests
 	unset CYTHON_FORCE_REGEN
 
+	# uses $(nproc) to additionally parallelize many OpenMP-based jobs,
+	# leading to overcommitting
+	local -x OMP_NUM_THREADS=1
+
 	tc-export CC
 
 	local testargs=(

dev-python/cython/cython-3.2.4.ebuild

@@ -69,6 +69,10 @@ python_test() {
 	# Needed to avoid confusing cache tests
 	unset CYTHON_FORCE_REGEN
 
+	# uses $(nproc) to additionally parallelize many OpenMP-based jobs,
+	# leading to overcommitting
+	local -x OMP_NUM_THREADS=1
+
 	tc-export CC
 
 	local testargs=(