pages*: use "an SQL" instead of "a SQL" (#12336)

pages/common/textql.md

@@ -3,7 +3,7 @@
 > Execute SQL against structured text like csv or tsv files.
 > More information: <https://github.com/dinedal/textql>.
 
-- Print the lines in the specified `.csv` file that match a SQL query to `stdout`:
+- Print the lines in the specified `.csv` file that match an SQL query to `stdout`:
 
 `textql -sql "{{SELECT * FROM filename}}" {{path/to/filename.csv}}`