Fix outdated Savannah URL for freetype download

[manasvi-sahare]

Fixes an outdated Savannah URL in subprojects/freetype-2.6.1.wrap.

The previous URL returned a 502 error. Updated it to use the working
savannah.nongnu.org mirror.

Closes #31340.

[timhoffm]

The nongnu.org is now the official download source for feetype.

https://freetype.org/download.html

Note: savannah.gnu.org is reserved for GNU packages, savannah.nongnu.org seems to be for other FOSS packages.

[QuLogic]

https://freetype.org/download.html

It's weird, because it shows nongnu.org, but the actual link is to gnu.org.

[timhoffm]

At least its listed on nongnu https://savannah.nongnu.org/projects/freetype.

And the download link there also goes to nongnu https://download.savannah.nongnu.org/releases/freetype/

[QuLogic]

I assume the distinction has been muddied over the years and it doesn't matter too much any more, i.e. https://savannah.gnu.org/projects/freetype redirects to nongnu.org as well. So I don't know why it helps, but if people think so, then I guess that's fine.