Add support for alpine 3.17, remove alpine 3.15

[squizzi]

This PR adds support for alpine 3.17 and removes support for 3.15 to adhere to the policy of only supporting two major releases.

[squizzi]

Apparently alpine:3.17 is still in RC stages so I jumped the gun a bit on this, but it should be out officially by end of week.

Edit: Andddd now it's released

[tianon]

Nice, thanks! 👍

We should also ditch this entire RUN line (and associated comments) now that we don't need to deal with 3.15 anymore: 👀

golang/Dockerfile-linux.template

Lines 13 to 22 in 326acd5

	# ensure that nsswitch.conf is set up for Go's "netgo" implementation
	# - https://github.com/golang/go/blob/go1.19.3/src/net/conf.go#L227-L303
	# - docker run --rm debian grep '^hosts:' /etc/nsswitch.conf
	# Alpine 3.16 includes nsswitch.conf
	RUN set -eux; \
	if [ -e /etc/nsswitch.conf ]; then \
	grep '^hosts: files dns' /etc/nsswitch.conf; \
	else \
	echo 'hosts: files dns' > /etc/nsswitch.conf; \
	fi

(I'm happy to take over and make this change if you would rather not do so!)

[squizzi]

We should also ditch this entire RUN line (and associated comments) now that we don't need to deal with 3.15 anymore: eyes

@tianon How's that look?

[tianon]

Nice thank you! (and thanks for sticking with it!)