test: Disable `error union switch with call operand` (ReleaseSafe) on macos.

This started failing in LLVM 20:

test
+- test-stack-traces
   +- check error union switch with call operand (ReleaseSafe llvm) failure
error:
========= expected this stdout: =========
error: TheSkyIsFalling
source.zig:3:5: [address] in [function]
    return error.TheSkyIsFalling;
    ^

========= but found: ====================
error: TheSkyIsFalling
source.zig:13:27: [address] in [function]
        error.NonFatal => return,
                          ^
7c85dc4602Alex Rønne Petersen committed on 4/4/2025, 4:08:10 AMparent4b360a1
1 file changedLine totals unavailable