Allow *.spx glob for audio/x-speex+ogg

Currently, *.spx is associated with "raw" speex, i.e. without an ogg
container, while it is also often used for audio/x-speex+ogg. The latter
currently only allows the *.oga and *.ogg globs.

See also

The libspeex speexenc/speexdec reference implementations use ogg
containers, and use the *.spx extension, see e.g.

"raw" speex and speex+ogg are covered by their content matches, i.e.
'OggS'@0 + 'Speex   '@28 vs. 'Speex   '@0.
Apparently the only application capable of creating "raw" speex is the xiph
sampleenc, see

Fixes #103
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Status Job ID Name Coverage
passed #2578134