On Linux/Unix based implementations, exec/cmd.Run will return either context.ContextCancelled or the error "signal: killed" depending on whether the cancellation occurred while the process was running.

There's several places we check on ```is.Errors(err, context.Cancelled)``` on whether to emit high level logs about failed program compilations.  Because already running cmd.Run() doesn't return an error that satisfies this, this will result in spurious error logs about failed compilation (i.e. "signal: killed")

This meant that in cases where a compilation is legitimately cancelled, we would still log an error such as

msg="BPF template object creation failed" ... error="...: compile bpf_lxc.o: signal: killed"

This can occur occasionally in CI, which enforces no error to pass, causing failures.

example:
```
	ctx, c := context.WithTimeout(context.Background(), time.Second)
	go func() {
		time.Sleep(time.Second)
		c()
	}()
	cmd := exec.CommandContext(ctx, "sleep", "2")
	fmt.Println(cmd.Run())

	ctx, c = context.WithTimeout(context.Background(), time.Second)
	c()
	cmd = exec.CommandContext(ctx, "sleep", "2")
	fmt.Println(cmd.Run())
```

To fix this, this will join in the ctx.Err() if it is:
* context.Cancelled
* The process has not exited itself.
* The process appeared to be SIGKILL'ed.

Addresses: #30991

Signed-off-by: Tom Hadlaw <tom.hadlaw@isovalent.com>