test: assert parsed port ranges

[immanuwell]

Tiny test hardening PR.

TestParsePortRange called reflect.DeepEqual but dropped the bool, so the test could go green even when the parsed range was wrong. small but real, imo.

Repro on main:

• change the first expected range in pkg/util/portrange_test.go from 23-23 to 24-24
• run go test ./pkg/util
• it still passes, which is not what we want

This makes the test fail on bad parsed ranges and on unexpected errors.

Validation:

• go test ./pkg/util
• go test ./pkg/inject ./pkg/util
• go vet ./pkg/util

[alpeb]

Thanks @immanuwell !