Set log level for APKBUILD parsing to verbose instead of debug

"pmbootstrap log" is a bit hard to read these days, with all the apkbuild parsing related messages. For example:

https://builds.sr.ht/~postmarketos/job/161152#task-pmbootstrap_build-160

(002270) [09:55:14] busybox-static-armhf: key '_arch' for replacing '$_arch' not found, ignoring
(002270) [09:55:14] busybox-static-armhf: key '_arch' for replacing '$_arch' not found, ignoring
(002270) [09:55:14] busybox-static-armhf: key '_mirror' for replacing '$_mirror' not found, ignoring
(002270) [09:55:14] busybox-static-armhf: key '_arch' for replacing '$_arch' not found, ignoring
(002270) [09:55:14] musl-aarch64: key '_arch' for replacing '$_arch' not found, ignoring
(002270) [09:55:14] musl-aarch64: key '_arch' for replacing '$_arch' not found, ignoring
(002270) [09:55:14] musl-aarch64: key '_mirror' for replacing '$_mirror' not found, ignoring
(002270) [09:55:14] musl-aarch64: key '_arch' for replacing '$_arch' not found, ignoring
(002270) [09:55:14] musl-aarch64: key '_arch' for replacing '$_arch' not found, ignoring

Let's change the log level from "debug" (not shown in stdout, but in "pmbootstrap log") to "verbose" (shown in "pmbootstrap log" only if pmbootstrap runs with -v). This can be done by modifying the appropriate logging.debug statements to logging.verbose.

@Minecrell, @z3ntu: I think we briefly discussed this in one MR - I don't remember the details and sort of need to go, but imho we can't leave this as-is and need to improve this to make logs readable again. Opinions?