Bump Go version to fix macOS resolver issue

[pziggo]

With Go version < 1.20, Go is using the internal Go DNS resolver by default
which only considers the file /etc/resolv.conf similar to glibc's behaviour.
But macOS also supports additional configurations under /etc/resolver which
is often used for local development to use proper name resolution.

The behaviour has been changed beginning with Go version 1.20
(see also https://go-review.googlesource.com/c/go/+/446178)

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Relates OR Closes #1940

Release note for CHANGELOG:

Add support for macOS resolver configuration

Output from acceptance testing:

$ go version
go version go1.20.6 darwin/amd64
$ make testacc TESTARGS='-run=TestAccXXX'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test -run=TestAccXXX -timeout 30m ./...
?       github.com/hashicorp/terraform-provider-vault   [no test files]
?       github.com/hashicorp/terraform-provider-vault/cmd/coverage      [no test files]
?       github.com/hashicorp/terraform-provider-vault/cmd/generate      [no test files]
?       github.com/hashicorp/terraform-provider-vault/generated [no test files]
ok      github.com/hashicorp/terraform-provider-vault/codegen   (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/datasources/transform/decode    (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/datasources/transform/encode    (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/alphabet    (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/role        (cached) [no tests to run]
?       github.com/hashicorp/terraform-provider-vault/helper    [no test files]
?       github.com/hashicorp/terraform-provider-vault/internal/consts   [no test files]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/template    (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/transformation      (cached) [no tests to run]
?       github.com/hashicorp/terraform-provider-vault/internal/identity/group   [no test files]
?       github.com/hashicorp/terraform-provider-vault/internal/identity/mfa     [no test files]
?       github.com/hashicorp/terraform-provider-vault/internal/pki      [no test files]
ok      github.com/hashicorp/terraform-provider-vault/internal/identity/entity  (cached) [no tests to run]
?       github.com/hashicorp/terraform-provider-vault/schema    [no test files]
ok      github.com/hashicorp/terraform-provider-vault/internal/provider (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/testutil  (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/util      (cached) [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/vault     0.955s [no tests to run]
...

[hashicorp-cla]

All committers have signed the CLA.

[heatherezell]

Thank you for this! OS X resolver issues have been a bit of a bear for a while. Our engineering team is including it in a review of dependencies, and we're tracking this PR with that. Thanks again!

[fairclothjm]

LGTM! Thanks @pziggo