Allow keywords as column names in ALTER UPDATE assignments

Column names like 'key' can be keywords. Allow keywords in addition to
identifiers when parsing UPDATE assignment column names.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

parser/parser.go

@@ -6034,7 +6034,8 @@ func (p *Parser) parseAlterCommand() *ast.AlterCommand {
 		p.nextToken() // skip UPDATE
 		// Parse assignments
 		for {
-			if !p.currentIs(token.IDENT) {
+			// Column name can be IDENT or keyword (e.g., key, value)
+			if !p.currentIs(token.IDENT) && !p.current.Token.IsKeyword() {
 				break
 			}
 			assign := &ast.Assignment{

parser/testdata/03731_null_parts_in_storage_snapshot_with_only_analyze/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt7": true
-  }
-}
+{}