[SPARK-45109][SQL][CONNECT][FOLLOWUP] Fix log function in Connect

### What changes were proposed in this pull request?
This is a follow-up PR to apache#42863, the 1 argument `log` function should also point to `ln`.

### Why are the changes needed?
Bugfix.

### Does this PR introduce _any_ user-facing change?
No, these Spark Connect functions haven't been released.

### How was this patch tested?
Exsiting UTs.

### Was this patch authored or co-authored using generative AI tooling?
No.

Closes apache#42869 from peter-toth/SPARK-45109-fix-log.

Authored-by: Peter Toth <peter.toth@gmail.com>
Signed-off-by: Peter Toth <peter.toth@gmail.com>

connector/connect/client/jvm/src/main/scala/org/apache/spark/sql/functions.scala

@@ -2632,7 +2632,7 @@ object functions {
    * @group math_funcs
    * @since 3.4.0
    */
-  def log(e: Column): Column = Column.fn("log", e)
+  def log(e: Column): Column = ln(e)
 
   /**
    * Computes the natural logarithm of the given column.

connector/connect/common/src/test/resources/query-tests/explain-results/function_log.explain

@@ -1,2 +1,2 @@
-Project [LOG(E(), b#0) AS LOG(E(), b)#0]
+Project [ln(b#0) AS ln(b)#0]
 +- LocalRelation <empty>, [id#0L, a#0, b#0, d#0, e#0, f#0, g#0]

connector/connect/common/src/test/resources/query-tests/queries/function_log.json

@@ -13,7 +13,7 @@
     },
     "expressions": [{
       "unresolvedFunction": {
-        "functionName": "log",
+        "functionName": "ln",
         "arguments": [{
           "unresolvedAttribute": {
             "unparsedIdentifier": "b"