SQL: [Docs] Small fixes for CURRENT_TIMESTAMP docs (#40792)

- Added square brackets for the optional argument of precision
- Fixed character to lower case after comma

(cherry picked from commit d2f6f3b)

Author: matriv

docs/reference/sql/functions/date-time.asciidoc

@@ -100,7 +100,7 @@ beta[]
 [source, sql]
 --------------------------------------------------
 CURRENT_TIMESTAMP
-CURRENT_TIMESTAMP(precision <1>)
+CURRENT_TIMESTAMP([precision <1>])
 --------------------------------------------------
 
 *Input*:
@@ -141,7 +141,7 @@ include-tagged::{sql-specs}/docs.csv-spec[filterNow]
 --------------------------------------------------
 
 [IMPORTANT]
-Currently, Using a _precision_ greater than 3 doesn't make any difference to the output of the
+Currently, using a _precision_ greater than 3 doesn't make any difference to the output of the
 function as the maximum number of second fractional digits returned is 3 (milliseconds).
 
 [[sql-functions-datetime-day]]