Why time period of GPS PPS signal is not accurately equal to 1 second. (7 to 10 mirco sec less)
This is definitively your computer clock that is inaccurate as you are using the Salae Logic Analyzer software.

7ppm is within the expected precision bounds for your computer clock's crystal.

You can expect the GPS clock of a commercial receiver to have an accuracy that is better than 1us - and I think that this is short and long term jitter accuracy.  The (absolute) precision actually depends on your receiver and meteorologic conditions.

More or less every 18 months, UTC time is adjusted so that a leaps seconds must be taken into account to convert the GPS clock to UTC time.
That is due to earth turning slower and slower.  This the precision of a second as these leap seconds only synchronise our calendar with the rotation of the earth.