Fix diagnostic comparison issues in s3 backend tests (#37509)

[SarahFrench]

Required to enable testing dependency changes on the v1.13 release branch that impact the backends (i.e. #37837)

Cherrypicking in the changes from #37509

Prior to this change s3 tests would fail due to the tests' expected diagnostics for comparison to actual diagnostics lacking tfdiags.SourceRange data:

--- FAIL: TestBackendConfig_DynamoDBEndpoint (5.66s)
    --- FAIL: TestBackendConfig_DynamoDBEndpoint/config_hostname (0.84s)
        backend_test.go:528: TestBackendConfig on *s3.Backend with configtesting.synthBody{Filename:"<TestWrapConfig>", Values:map[string]cty.Value{"bucket":cty.StringVal("tf-test"), "endpoints":cty.ObjectVal(map[string]cty.Value{"dynamodb":cty.StringVal("dynamo.test")}), "key":cty.StringVal("state"), "region":cty.StringVal("us-west-1")}}
        backend_test.go:532: unexpected diagnostics difference:   tfdiags.Diagnostics{
            -   &tfdiags.attributeDiagnostic{
            -           diagnosticBase: tfdiags.diagnosticBase{
            -                   severity: s"Warning",
            -                   summary:  "Complete URL Expected",
            -                   detail:   "The value should be a valid URL containing at least a scheme and"...,
            -           },
            -           attrPath: cty.Path{cty.GetAttrStep{Name: "endpoints"}, cty.GetAttrStep{Name: "dynamodb"}},
            -           subject: &tfdiags.SourceRange{
            -                   Filename: "<TestWrapConfig>",
            -                   Start:    tfdiags.SourcePos{Line: 1, Column: 1},
            -                   End:      tfdiags.SourcePos{Line: 1, Column: 1},
            -           },
            -   },
            +   &tfdiags.attributeDiagnostic{
            +           diagnosticBase: tfdiags.diagnosticBase{
            +                   severity: s"Warning",
            +                   summary:  "Complete URL Expected",
            +                   detail:   "The value should be a valid URL containing at least a scheme and"...,
            +           },
            +           attrPath: cty.Path{cty.GetAttrStep{Name: "endpoints"}, cty.GetAttrStep{Name: "dynamodb"}},
            +   },
              }

Following this PR the tests pass, as the expected diagnostics match (comparison no longer expects tfdiags.SourceRange data):

$ TF_ACC=1 go test -count=1 ./...
ok      github.com/hashicorp/terraform/internal/backend/remote-state/s3 319.384s

Target Release

1.13.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

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