test(process): use /bin/sh not /bin/true (absent on macOS)

The macOS CI failures across every launcher attempt were this test, not the
implementation: /bin/true lives at /usr/bin/true on macOS, so run_exec returned
127 and the rc==0 assertion failed. Use /bin/sh -c 'exit 0' (present on Linux
and macOS).

Author: Sunrisepeak

tests/unit/test_process_run_exec.cpp

@@ -17,7 +17,9 @@ using namespace mcpp::platform;
 // into /bin/sh and crashed it on newer-glibc hosts.
 TEST(RunExec, DoesNotMutateParentEnvironment) {
     ::setenv("MCPP_TEST_LEAK", "sentinel", 1);
-    int rc = process::run_exec({"/bin/true"},
+    // Use /bin/sh (present on Linux AND macOS) — /bin/true lives at
+    // /usr/bin/true on macOS, so it is not a portable launch target.
+    int rc = process::run_exec({"/bin/sh", "-c", "exit 0"},
                                {{"MCPP_TEST_LEAK", "injected"}});
     EXPECT_EQ(rc, 0);
     const char* v = ::getenv("MCPP_TEST_LEAK");