Fix to handling of packages with caps

[jonathon-love]

Currently flatpak builder doesn't handle packages with caps in them properly. i.e. it does not generate the sources appropriately for, say, PyYAML.

[dreua]

In which way did it generate the sources wrong?
In the case of pikepdf this change results in Deprecated (package name with capital D) vanishing from the generated sources. I now have to figure out if that should never have been there in the first place or if it is now missing due to the change.
https://github.com/dreua/flatpak-module-qpdf-pikepdf/pull/84/files

[dreua]

I think this is a regression, pikepdf now fails to build because Deprecated is missing in the newly generated dependencies.
Are you sure the keys in sources are casefolded? I guess they aren't but haven't run the debugger on it.

[bbhtt]

Try #429

[dreua]

I just came up with the very small change in #430 which works for me. Now I see #429 which looks a lot more complex. Not sure what issues it needs to solve though, maybe that complexity is necessary.

[dreua]

There is a difference in the x-checker-data, but the data checker doesn't seem to care:

         x-checker-data:
-          name: Deprecated [my version and the status quo before this regression]
+          name: deprecated [@bbhtt's version]

[bbhtt]

because you are lowercasing it in only one place - sources, anyway that doesn't cause any functional difference.