Consolidate use of Go 1.18

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

Author: Paulo Gomes

.github/workflows/release.yaml

@@ -156,7 +156,7 @@ jobs:
           fetch-depth: 0
       - uses: actions/setup-go@v3
         with:
-          go-version: 1.17.x
+          go-version: 1.18.x
       - name: Setup Cosign
         uses: sigstore/cosign-installer@main
       - name: Setup Syft

Dockerfile.libgit2-only

@@ -1,7 +1,7 @@
 # This Dockerfile builds and packages libgit2 only (not linked with openssl and libssh2)
 
 ARG BASE_VARIANT=alpine
-ARG GO_VERSION=1.17
+ARG GO_VERSION=1.18
 ARG XX_VERSION=1.1.0
 
 FROM --platform=$BUILDPLATFORM tonistiigi/xx:${XX_VERSION} AS xx

Dockerfile.test-libgit2-only

@@ -1,7 +1,7 @@
 # This Dockerfile builds and packages libgit2 only (not linked with openssl and libssh2); and tests it against git2go.
 
 ARG BASE_VARIANT=alpine
-ARG GO_VERSION=1.17
+ARG GO_VERSION=1.18
 ARG XX_VERSION=1.1.0
 
 FROM --platform=$BUILDPLATFORM tonistiigi/xx:${XX_VERSION} AS xx

tests/smoketest/go.mod

@@ -1,6 +1,6 @@
 module github.com/fluxcd/golang-with-libgit2/tests/sample
 
-go 1.17
+go 1.18
 
 require (
 	github.com/fluxcd/pkg/gittestserver v0.5.2