set VAULT_AUTH_CONFIG_GITHUB_TOKEN on vault container to avoid GH rate limit when running acceptance tests

[raymonstah]

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Relates OR Closes #0000

Release note for CHANGELOG:

NONE

Output from acceptance testing:

$ 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   0.677s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/datasources/transform/decode    0.385s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/datasources/transform/encode    0.578s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/alphabet    0.788s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/role        1.217s [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]
?       github.com/hashicorp/terraform-provider-vault/internal/identity/group   [no test files]
?       github.com/hashicorp/terraform-provider-vault/internal/pki      [no test files]
?       github.com/hashicorp/terraform-provider-vault/internal/identity/mfa     [no test files]
?       github.com/hashicorp/terraform-provider-vault/schema    [no test files]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/template    0.910s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/generated/resources/transform/transformation      0.401s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/internal/identity/entity  0.510s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/internal/provider 0.728s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/testutil  0.804s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/util      0.906s [no tests to run]
ok      github.com/hashicorp/terraform-provider-vault/vault     0.616s [no tests to run]

[raymonstah]

Note the acceptance tests will still fail since the vault versions are pinned. See hashicorp/vault#19244 for the fix