install_pmbootstrap.sh: add procps to depends

Let pmbootstrap properly kill processes that are timing out, instead of
having it display the busybox ps usage screen (as we are using arguments
of ps that busybox ps does not support):

[00:15:45] Process did not write any output for 900 seconds. Killing it.
[00:15:45] NOTE: The timeout can be increased with 'pmbootstrap -t'.
ps: unrecognized option: noheaders
BusyBox v1.31.1 () multi-call binary.
Usage: ps [-o COL1,COL2=HEADER]
Show list of processes
	-o COL1,COL2=HEADER	Select columns for display
[00:15:45] ERROR: Command '['ps', '-e', '-o', 'pid=,ppid=', '--noheaders']' returned non-zero exit status 1.

Example: https://gitlab.com/postmarketOS/pmaports/-/jobs/517281598#L6026

install_pmbootstrap.sh

@@ -19,6 +19,7 @@ fi
 depends="coreutils
 	git
 	openssl
+	procps
 	python3
 	sudo
 	$*"