test: Fix failure in TestAccCredentialStoreVault

[moduli]

ICU-11525

Originally, the test TestAccCredentialStoreVault was flaky for the following reason

=== RUN TestAccCredentialStoreVault
resource_credential_store_vault_test.go:101: Step 1/8 error: Error running apply: exit status 1
Error: error creating credential store: {"kind":"Internal", "message":"credentialstores.(Service).createInRepo: unable to create credential store: vault.(Repository).CreateCredentialStore: unable to lookup vault token: vault.(client).lookupToken: vault: http://localhost:32796: unknown: error #0: Error making API request.\n\nURL: GET http://localhost:32796/v1/auth/token/lookup-self\nCode: 400. Raw Message:\n\nClient sent an HTTP request to an HTTPS server.\n"}
with boundary_credential_store_vault.example,
on terraform_plugin_test.tf line 44, in resource "boundary_credential_store_vault" "example":
44: resource "boundary_credential_store_vault" "example" {

After pulling in boundary 0.14.3, which included this fix: hashicorp/boundary#3973, the test started to always fail for the following reason

resource_credential_store_vault_test.go:101: Step 3/8 error: Error running apply: exit status 1
Error: error updating credential store: {"kind":"Internal","message":"credentialstores.(Service).updateInRepo: unable to update credential store: vault.(Repository).UpdateCredentialStore: cannot lookup token for updated store: vault.(client).lookupToken: vault: https://localhost:32800: unknown: error #0: Get "https://localhost:32800/v1/auth/token/lookup-self\": tls: failed to verify certificate: x509: certificate is valid for localhost, not www.updated.com"}
with boundary_credential_store_vault.example,
on terraform_plugin_test.tf line 44, in resource "boundary_credential_store_vault" "example":
44: resource "boundary_credential_store_vault" "example" {

So, I think 0.14.3 included a fix for the original flaky behavior, but then exposed an issue with the test (the test server sets up a certificate that's only valid for localhost, but we're setting the server name to be www.updated.com).

This PR also includes an adjustment in the GitHub Action to disable caching in the setup-go step. We already handle caching in the Set up Go modules cache step, and without this adjustment, we were getting duplicate caching, resulting in errors like

Error: /usr/bin/tar: ../../../go/pkg/mod/go.mongodb.org/[email protected]/version/version.go: Cannot open: File exists
Error: /usr/bin/tar: ../../../go/pkg/mod/go.mongodb.org/[email protected]/bson/bsontype/bsontype_test.go: Cannot open: File exists
Error: /usr/bin/tar: ../../../go/pkg/mod/go.mongodb.org/[email protected]/bson/bsontype/bsontype.go: Cannot open: File exists

[elimt]

Thanks for looking at this so quickly!