[lldb] fix lldb-server test failures on windows (#164843)

Fix windows test failures from
https://github.com/llvm/llvm-project/pull/162730 by including and
optional .exe on the lldb-server name. Still passes on linux, but should
pass on windows now.

```
> bin/llvm-lit -v tools/lldb/test/Shell/lldb-server/
llvm-lit: llvm-project/llvm/utils/lit/lit/llvm/config.py:531: note: using clang: llvm-project/build/bin/clang
llvm-lit: llvm-project/llvm/utils/lit/lit/llvm/config.py:531: note: using ld.lld: /usr/bin/ld.lld
llvm-lit: llvm-project/llvm/utils/lit/lit/llvm/config.py:531: note: using lld-link: /usr/bin/lld-link
llvm-lit: llvm-project/llvm/utils/lit/lit/llvm/config.py:531: note: using ld64.lld: /usr/bin/ld64.lld
llvm-lit: llvm-project/llvm/utils/lit/lit/llvm/config.py:531: note: using wasm-ld: /usr/bin/wasm-ld
llvm-lit: llvm-project/llvm/utils/lit/lit/llvm/subst.py:126: note: Did not find obj2yaml in llvm-project/build/./bin:llvm-project/build/./bin
llvm-lit: llvm-project/llvm/utils/lit/lit/llvm/subst.py:126: note: Did not find llvm-objdump in llvm-project/build/./bin:llvm-project/build/./bin
llvm-lit: llvm-project/lldb/test/Shell/lit.cfg.py:125: warning: Could not set a default per-test timeout. Requires the Python psutil module but it could not be found. Try installing it via pip or via your operating system's package manager.
-- Testing: 4 tests, 4 workers --
PASS: lldb-shell :: lldb-server/TestGdbserverErrorMessages.test (1 of 4)
PASS: lldb-shell :: lldb-server/TestPlatformHelp.test (2 of 4)
PASS: lldb-shell :: lldb-server/TestPlatformErrorMessages.test (3 of 4)
PASS: lldb-shell :: lldb-server/TestPlatformSuccessfulStartup.test (4 of 4)

Testing Time: 1.10s

Total Discovered Tests: 4
  Passed: 4 (100.00%)

1 warning(s) in tests
```

0 files changed, 0 insertions, 0 deletions