fix: typo in static query WHERE clause example

[vcrfxia]

Description

Issuing a static query with WINDOWSTART bounds of the form WHERE a < WINDOWSTART AND WINDOWSTART < b returns in the error:

Server failed to execute statement
statement: 
reason: Unsupported WINDOWSTART bounds: [GREATER_THAN]
Static queries currently require a WHERE clause that:
 - limits the query to a single ROWKEY, e.g. `SELECT * FROM X WHERE ROWKEY=Y;`.
 - limits the time bounds of the windowed table. This can be: 
    + a single window lower bound, e.g. `WHERE WINDOWSTART = z`, or
    + a range, e.g. `WHERE a < WINDOWSTART AND WINDOWSTART < b
WINDOWSTART currently supports operators: [EQUAL, GREATER_THAN_OR_EQUAL, LESS_THAN]
WINDOWSTART currently comparison with epoch milliseconds or a datetime string in the form: yyyy-MM-dd'T'HH:mm:ss.SSS

This PR updates the error message to show what the form of the bounds actually needs to be.

Testing done

Non-functional change.

Reviewer checklist

• Ensure docs are updated if necessary. (eg. if a user visible feature is being added or changed).
• Ensure relevant issues are linked (description should include text like "Fixes #")

[big-andy-coates]

Good catch - thanks Vic!