[raster] Errors in examples of doc for ST_Neighborhood

[lrohr]

I spotted 3 errors in the examples cited in the documentation for ST_Neighborhood:

• First example: The result should be {{NULL,1,1},{1,1,1},{1,NULL,1}}. Reproduce: Execute query (copy-paste) on a server.

• Third example: There is a "SELECT" missing between lines 5 and 6. Copy-pasting the query as is raises a syntax error. Correct:

  FROM (
  	SELECT
  		ST_SetValues(
  

• Third example: The result should be {{1,1,0},{0,1,1},{1,1,1}}. Reproduce: Execute query (copy-paste) with the correction above on a server.

[Regina Obe <lr@…>]

In 25825b6/git:

Fix ST_Neighborhood docs references #3933 for PostGIS 3.1

[Regina Obe <lr@…>]

In 867636c/git:

Fix ST_Neighborhood docs references #3933 for PostGIS 3.0

[Regina Obe <lr@…>]

In 88f81843/git:

Fix ST_Neighborhood docs closes #3933 for PostGIS 2.5.5