[fix](fe) Fix GroupJoin session variable annotation

### What problem does this PR solve?

Issue Number: None

Related PR: None

Problem Summary: The GroupJoin session variable used a string array for the description attribute, but VarAttr accepts a single string. This caused FE compilation to fail and prevented annotation processors from generating methods used throughout fe-core. Use a single English description string supported by the annotation.

### Release note

None

### Check List (For Author)

- Test: Build FE
    - `sh build.sh --fe -j48`
- Behavior changed: No
- Does this need documentation: No

fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java

diff --git a/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java b/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
index bfa2600..199d84f 100644
--- a/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
+++ b/fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java
@@ -1110,11 +1110,9 @@
     // join and aggregation, eliminating the need for a separate aggregation pass.
     @VarAttrDef.VarAttr(name = "enable_group_join_fusion", needForward = true,
             varType = VariableAnnotation.EXPERIMENTAL,
-            description = {"是否启用 GroupJoin 融合算子（实验特性）。"
-                    + "当 GROUP BY 键与 equi-join 键等价时，将 INNER hash join 与 hash agg 融合为单个算子",
-                    "Enable GroupJoin fusion (experimental). "
+            description = "Enable GroupJoin fusion (experimental). "
                     + "Fuse INNER hash join + hash agg into a single operator when GROUP BY keys "
-                    + "are equivalent to equi-join keys"})
+                    + "are equivalent to equi-join keys")
     public boolean enableGroupJoinFusion = false;
 
     public boolean isEnableGroupJoinFusion() {