Fix $BUILD_VERSION not being passed to build-inside-vm.sh

Fixes: 3bda5b26 ("Use new experimental VM runners[1] for building")
6 jobs for master in 7 minutes and 45 seconds (queued for 6 seconds)
latest
Status Name Job ID Coverage
  Lint
passed shellcheck #37808

00:00:11

passed shfmt #37809

00:00:07

 
  Build
passed build:secure #37810
secure vm

00:03:16

 
  Test
passed test-basic-qemu #37812
fast-single-thread

00:03:09

passed test-cloudimg-qemu #37813
fast-single-thread

00:04:15

passed test-vagrant-boxes-format #37811

00:00:26