[SPARK-54450][FOLLOWUP] Relax the restriction of run-tests

### What changes were proposed in this pull request?

Relax the restriction on `run-tests.py`. Ultimately the tests are executed using a potentially different python under different environment. If we can't find anything, just pass it as it is, instead of stopping users from running it.

### Why are the changes needed?

It might break users' workflow when they have some weird setup. (Completely different python for `run-tests.py` and `bin/pyspark`)

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

Maually tested that a non-exist module will be passed to `bin/pyspark`.

### Was this patch authored or co-authored using generative AI tooling?

No

Closes #53292 from gaogaotiantian/relax-run-tests.

Authored-by: Tian Gao <[email protected]>
Signed-off-by: Ruifeng Zheng <[email protected]>

Author: gaogaotiantian

python/run-tests.py

@@ -237,11 +237,8 @@ def module_exists(module):
     for testname in testnames.split(','):
         if " " in testname:
             # "{module} {class.testcase_name}"
-            module, testcase = testname.split(" ")
-            if not module_exists(module):
-                print(f"Error: Can't find module '{module}'.")
-                sys.exit(-1)
-            testnames_to_test.append(f"{module} {testcase}")
+            # Just add the testname as is
+            testnames_to_test.append(testname)
         else:
             if module_exists(testname):
                 # "{module}"
@@ -255,8 +252,8 @@ def module_exists(module):
                         testnames_to_test.append(f"{module} {testcase}")
                         break
                 else:
-                    print(f"Error: Invalid testname '{testname}'.")
-                    sys.exit(-1)
+                    # "Can't find the module, the users must know what they are doing"
+                    testnames_to_test.append(testname)
 
     return testnames_to_test