fix: update PHP prebuilt binary, version 7.4.15

[alexander-fenster]

Using googleapis Docker image 20220222, now with curl enabled. Replaces #462.

[noahdietz]

This will ensure that the binary works inside our specific docker image, but not necessarily when run from a linux workstation or other docker images (unless OwlBot, etc. us the same image). I wonder if we need to include more cached binaries to improve performance in those use cases. Speeding up the kokoro runs is definitely most important though.

[alexander-fenster]

not necessarily when run from a linux workstation

I actually checked that it works on a Linux workstation (in its current state).

other docker images

Yes, we need to regularly update them all.

[noahdietz]

I actually checked that it works on a Linux workstation (in its current state).

Awesome! Thank you for doing that.