Fix incorrect delimator ";" used to separate proj_info().searchpath entries

[nyalldawson]

... on non-windows platforms, should be ":", not ";"

[nyalldawson]

Refs qgis/QGIS#30048

[rouault]

@kbevers Do you think we should change the behaviour or keep as it ? After all, the implementation and documentation are consistent currently.
It is true that if we do the analogy with PATH, semi-colon for Windows and colon for Unix are more common.
When looking at the code, I was confused by the fact that path_append() has a #ifdef WIN32 / #else to have a different separator, but it isn't actually used

[kbevers]

Do you think we should change the behaviour or keep as it ? After all, the implementation and documentation are consistent currently.
It is true that if we do the analogy with PATH, semi-colon for Windows and colon for Unix are more common.

I think we should accept this PR. As you say, it conforms to normal practice. I believe this is also how we deal with delimeters when parsing PROJ_LIB, right?

When looking at the code, I was confused by the fact that path_append() has a #ifdef WIN32 / #else to have a different separator, but it isn't actually used

That is clearly a bug - delim should have been used in the first place.