Revert changes in functional/test_runner.py

test/functional/test_runner.py

@@ -594,7 +594,7 @@ def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=
         print(f"{BOLD[1]}WARNING!{BOLD[0]} There may be insufficient free space in {tmpdir} to run the Bitcoin functional test suite. "
               f"Running the test suite with fewer than {min_space // (1024 * 1024)} MB of free space might cause tests to fail.")
 
-    tests_dir = build_dir + '/test/functional/'
+    tests_dir = src_dir + '/test/functional/'
     # This allows `test_runner.py` to work from an out-of-source build directory using a symlink,
     # a hard link or a copy on any platform. See https://github.com/bitcoin/bitcoin/pull/27561.
     sys.path.append(tests_dir)