pmb.build: install checkdepends when building (MR 2563)

Fixes a bug where checkdepends are not being installed, and packages
that run tests that depend on something in checkdepends fail because
it's missing. For example, the `plasma-workspace` forked pkg in pmaports
tells abuild to run `xwfb-run` in `check()`, this binary comes from
`xwayland-run`, which is listed in the `checkdepends`. However this
isn't being installed and so `pmb build` ultimately fails to build the
package.

pmb/build/_package.py

@@ -694,6 +694,8 @@ def packages(
                     " adjust your APKBUILD to specify host dependencies (e.g. libevdev-dev)"
                     " and build dependencies (e.g. meson) separately."
                 )
+        if "!check" not in apkbuild["options"]:
+            depends_build += apkbuild["checkdepends"]
         if depends_host:
             logging.info("*** Install host dependencies")
             pmb.chroot.apk.install(depends_host, hostchroot, build=False)