Fix the "=" operator should be present if the setting variable carries a value

[laojianzi]

ref: https://clickhouse.com/docs/en/sql-reference/statements/alter/role

This syntax may be an error

ALTER ROLE r3_01293 SETTINGS max_memory_usage 5000000;

[coveralls]

Pull Request Test Coverage Report for Build 9954530352

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 12 of 20 (60.0%) changed or added relevant lines in 4 files are covered.
• 1383 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.2%) to 58.276%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/parser_column.go	1	2	50.0%
parser/parse_system.go	8	10	80.0%
parser/ast.go	1	6	16.67%

Files with Coverage Reduction	New Missed Lines	%
parser/parser_column.go	20	61.01%
parser/parser_query.go	28	61.91%
parser/parser_alter.go	79	72.27%
parser/ast.go	1256	54.11%

Totals
Change from base Build 9949491275:	0.2%
Covered Lines:	5950
Relevant Lines:	10210

---

💛 - Coveralls

[git-hulk]

LGTM, thanks