Doesn’t void warranty.
However, Apple’s 1 year limited warranty does not cover accidental damages or cosmetic damages/wear like dents and scratches.
Worth noting that if there is a dent somewhere on the device and your Mac isn’t working as expected, e.g. dent on bottom case near hinges and your display flickers, you might be asked to pay for the repair as the dent might be attributed to the screen flicker, noting that this does not mean your warranty is void, just merely means you might have damaged the Mac so it’s not covered. Check your Mac in to the Apple Retail Store for a diagnosis if you’re having problems.