Empty GLOBAL VARIABLES version in nighty version

[Ehco1996]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

MySQL [(none)]> SHOW GLOBAL VARIABLES LIKE "version";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| version       |       |
+---------------+-------+
1 row in set, 1 warning (0.00 sec)

2. What did you expect to see? (Required)

show normal version like

mysql> SHOW GLOBAL VARIABLES LIKE "version";
+---------------+-------------------------------------------+
| Variable_name | Value                                     |
+---------------+-------------------------------------------+
| version       | 5.7.25-TiDB-v4.0.0-beta.2-2953-gb91aeedab |
+---------------+-------------------------------------------+
1 row in set (0.00 sec)

3. What did you see instead (Required)

empty version

4. What is your TiDB version? (Required)

./tidb-server -V

Release Version: v5.3.0-alpha-7-g4c49e5204
Edition: Community
Git Commit Hash: 4c49e5204fb60b01a76b78619eb6627a1a387a71
Git Branch: master
UTC Build Time: 2021-09-02 12:53:36
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

SELECT tidb_version()

| Release Version: v5.3.0-alpha-7-g4c49e5204
Edition: Community
Git Commit Hash: 4c49e5204fb60b01a76b78619eb6627a1a387a71
Git Branch: master
UTC Build Time: 2021-09-02 12:53:36
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |

[Defined2014]

I think it's caused by #27731. Sorry, I will fix it.

[Defined2014]

/assign

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