Debugger: (Re-)Fix start of Android lldb from NDK 23.x on Linux

In order to help lldb locate libpython3.9.so, we need to point
LD_LIBRARY_PATH to the right lib/ path inside the NDK.

Amends: b54bf8ad86

Reason for amend: The "prepend" use-case of Environment::prependOrSet
failed due to the undefined separator. Now, use
Environment::prependOrSetLibrarySearchPath instead, since that handles
the separator and knows the environment variable name.

Fixes: QTCREATORBUG-27297
Change-Id: I770a6335a7a26c65d23c930f7d6f9795b3dc52b5
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/debugger/debuggeritem.cpp

@@ -294,7 +294,7 @@ bool DebuggerItem::addAndroidLldbPythonEnv(const Utils::FilePath &lldbCmd, Utils
             if (HostOsInfo::isAnyUnixHost()) {
                 const FilePath pythonLibDir = pythonDir.pathAppended("lib");
                 if (pythonLibDir.exists())
-                    env.prependOrSet("LD_LIBRARY_PATH", pythonLibDir.toString());
+                    env.prependOrSetLibrarySearchPath(pythonLibDir);
             }
 
             return true;