[Doc] modify irregular documents (like/ not like/ regexp.md) (#6572)

docs/en/sql-reference/sql-functions/string-functions/regexp/not_regexp.md

@@ -28,7 +28,7 @@ under the license.
 ## description
 ### syntax
 
-'BOOLEAN not regexp(VARCHAR str, VARCHAR pattern)'
+`BOOLEAN not regexp(VARCHAR str, VARCHAR pattern)`
 
 Perform regular matching on the string str, return false if it matches, and return true if it doesn't match. pattern is a regular expression.
 

docs/en/sql-reference/sql-functions/string-functions/regexp/regexp.md

@@ -28,7 +28,7 @@ under the License.
 ## description
 ### syntax
 
-'BOOLEAN regexp(VARCHAR str, VARCHAR pattern)'
+`BOOLEAN regexp(VARCHAR str, VARCHAR pattern)`
 
 Perform regular matching on the string str, return true if it matches, and return false if it doesn't match. pattern is a regular expression.
 

docs/en/sql-reference/sql-functions/string-functions/regexp/regexp_replace.md

@@ -28,7 +28,7 @@ under the License.
 ## description
 ### Syntax
 
-`VARCHAR regexp_replace(VARCHAR str, VARCHAR pattern, VARCHAR repl)
+`VARCHAR regexp_replace(VARCHAR str, VARCHAR pattern, VARCHAR repl)`
 
 
 Regular matching of STR strings, replacing the part hitting pattern with repl