testing/py3-litex: avoid global exec

Shelling out in the global scope is expensive and in this case not
necessary, change the `cut` invocation to parameter substitution.

`${foo%:*}` cuts of the `:` and everything that comes after it, which is
the same as `| cut -d : -f 1` does.

testing/py3-litex/APKBUILD

@@ -74,13 +74,13 @@ _cores_litex_hub="
 _cores="$_cores_enjoy_digital $_cores_litex_hub"
 
 for _core_name in $_cores_enjoy_digital; do
-	_core=$(echo "$_core_name" | cut -d : -f 1)
+	_core=${_core_name%:*}
 	subpackages="$subpackages py3-lite$_core:_subpkg_core"
 	source="$source py3-lite$_core-$pkgver.tar.gz::https://github.com/enjoy-digital/lite$_core/archive/refs/tags/$pkgver.tar.gz"
 done
 
 for _core_name in $_cores_litex_hub; do
-	_core=$(echo "$_core_name" | cut -d : -f 1)
+	_core=${_core_name%:*}
 	subpackages="$subpackages py3-lite$_core:_subpkg_core"
 	source="$source py3-lite$_core-$pkgver.tar.gz::https://github.com/litex-hub/lite$_core/archive/refs/tags/$pkgver.tar.gz"
 done