You can't put IO pins of a single MCU in series, so greater voltage is unachievable. IO pin also do not provide enough current anyway to drive a typical relay coil, so you need to drive a transistor with the IO pin, and let the transistor drive higher currents and/or voltages of the coil.
Just to make sure, the OJE-SH-105DW relay coil is rated for 55.6 ohms, at 5V, which is 450mW, so it would like to consume about 90 milliamperes.
For comparison, the Arduino 5V GPIO pins are rather strong, but they still have absolute maximum rating of 40mA, which is a limit that must not be exceeded during normal operation to prevent immediate or long-term damage.
It has an electrical specification that guarantees that the GPIO pin can provide 20mA under normal conditions, and voltage will have dropped to about 4V at that current. The tiny transistor providing the current will then heat up at 20mW, so only 80mW is provided to your load.
Beyond the guaranteed 20mA, the circuit is not guaranteed to work, it may or may not work depending on manufacturing tolerances, temperature, supply voltage, etc, and it would heat up the tiny transistor too much.
The 5V you are measuring from GPIO pin must be without load, I'd expect it will be much lower when the relay is connected.