[clang] [llvm] workflows/release-binaries: Disable flang on Darwin (PR #164667)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-test-suite` running on `ppc64le-clang-test-suite` while building `.github,clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/95/builds/18971

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
PASS: mlgo-utils :: corpus/extract_ir_script.test (103444 of 103455)
PASS: LLVM :: CodeGen/ARM/build-attributes.ll (103445 of 103455)
PASS: SanitizerCommon-lsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (103446 of 103455)
PASS: SanitizerCommon-asan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (103447 of 103455)
PASS: SanitizerCommon-msan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (103448 of 103455)
PASS: SanitizerCommon-tsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (103449 of 103455)
PASS: SanitizerCommon-ubsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (103450 of 103455)
PASS: LLVM :: tools/llvm-objdump/ELF/AMDGPU/subtarget.ll (103451 of 103455)
PASS: LLVM :: tools/llvm-readobj/ELF/file-header-machine-types.test (103452 of 103455)
PASS: Clang :: Driver/fsanitize.c (103453 of 103455)
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=7019.679112

```

</details>

https://github.com/llvm/llvm-project/pull/164667