fix: fix postgresql golden tests (#866)

Fix bug in PostgreSQL golden test parsing where the test case buffers
were not cleaned up after a test case finished.

test_data/goldens/postgres/create_table.test

@@ -1,3 +1,17 @@
+CREATE TABLE "table-with-invalid-chars$%^&" (
+    id bigint
+);
+ALTER TABLE "table-with-invalid-chars$%^&" ADD PRIMARY KEY (id)
+--
+CREATE TABLE `table_with_invalid_chars____` (
+    `id` INT64 NOT NULL ,
+) PRIMARY KEY (`id`)
+--
+CREATE TABLE table_with_invalid_chars____ (
+    id INT8 NOT NULL ,
+    PRIMARY KEY (id)
+)
+==
 CREATE TABLE test (
     id bigint PRIMARY KEY,
     col text

testing/common/goldens.go

@@ -74,6 +74,9 @@ func GoldenTestCasesFrom(path string) ([]GoldenTestCase, error) {
 				ExpectedGSQLSchema: sanitizedGSQLSchema,
 				ExpectedPSQLSchema: sanitizedPSQLSchema})
 			parsingStatus = InputSchema
+			inputSchema.Reset()
+			expectedGSQLSchema.Reset()
+			expectedPSQLSchema.Reset()
 			continue
 		}