Disable tests that do real requests to lyrics sites by default.
Disable tests that do real requests to lyrics sites by default.

Set BEETS_TEST_LYRICS_SOURCES environment variable to '1' to not skip the
tests.

beetbox/beets,pkess/beets,jackwilsdon/beets,shamangeorge/beets,pkess/beets,beetbox/beets,ibmibmibm/beets,SusannaMaria/beets,sampsyo/beets,SusannaMaria/beets,Kraymer/beets,ibmibmibm/beets,sampsyo/beets,pkess/beets,jackwilsdon/beets,shamangeorge/beets,beetbox/beets,SusannaMaria/beets,beetbox/beets,Kraymer/beets,Kraymer/beets,sampsyo/beets,SusannaMaria/beets,shamangeorge/beets,Kraymer/beets,sampsyo/beets,ibmibmibm/beets,shamangeorge/beets,jackwilsdon/beets,jackwilsdon/beets,ibmibmibm/beets,pkess/beets