Update Go to 1.16

This commit updates Go to 1.16, a required change because of the use of
`os.WriteFile` in one of the tests introduced by commit
b5004a93bc.

Normally _just_ this would not justify the change, but given the
introduction of breaking changes (and thereby forcing a MINOR update
anyway), and the various file{system, path} improvements introduced in
Go 1.16 like
[`filepath#WalkDir`](https://golang.org/pkg/path/filepath/#WalkDir),
going ahead with this should be fine.

Signed-off-by: Hidde Beydals <hello@hidde.co>

.github/actions/run-tests/Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.15-alpine
+FROM golang:1.16-alpine
 
 # Add any build or testing essential system packages
 RUN apk add --no-cache build-base git pkgconf

Dockerfile

@@ -1,5 +1,5 @@
 # Docker buildkit multi-arch build requires golang alpine
-FROM golang:1.15-alpine as builder
+FROM golang:1.16-alpine as builder
 
 RUN apk add gcc pkgconfig libc-dev
 RUN apk add --no-cache musl~=1.2 libgit2-dev~=1.1

api/go.mod

@@ -1,6 +1,6 @@
 module github.com/fluxcd/source-controller/api
 
-go 1.15
+go 1.16
 
 require (
 	github.com/fluxcd/pkg/apis/meta v0.8.0

go.mod

@@ -1,6 +1,6 @@
 module github.com/fluxcd/source-controller
 
-go 1.15
+go 1.16
 
 replace github.com/fluxcd/source-controller/api => ./api