ci: Run numeric tests in release mode to speed them up

Somehow, these take 30m on powerpc, which is too slow (much slower than
anything else.)

Author: bluss

scripts/cross-tests.sh

@@ -11,4 +11,4 @@ cross build -v --features="$FEATURES" --target=$TARGET
 cross test -v --no-fail-fast --features="$FEATURES" --target=$TARGET
 cross test -v --no-fail-fast --target=$TARGET --manifest-path=ndarray-rand/Cargo.toml --features quickcheck
 cross test -v --no-fail-fast --target=$TARGET --manifest-path=xtest-serialization/Cargo.toml --verbose
-cross test -v --no-fail-fast --target=$TARGET --manifest-path=xtest-numeric/Cargo.toml
+cross test -v --no-fail-fast --target=$TARGET --manifest-path=xtest-numeric/Cargo.toml --release