s3: check for EnvAWS credentials before Static credentials

EnvAWS considers more environment variables, including AWS_SESSION_TOKEN
and thus should be checked first.

internal/backend/s3/s3.go

@@ -107,13 +107,13 @@ func getCredentials(cfg Config) (*credentials.Credentials, error) {
 	//    call to a pre-defined endpoint, only valid inside
 	//    configured ec2 instances)
 	creds := credentials.NewChainCredentials([]credentials.Provider{
+		&credentials.EnvAWS{},
 		&credentials.Static{
 			Value: credentials.Value{
 				AccessKeyID:     cfg.KeyID,
 				SecretAccessKey: cfg.Secret.Unwrap(),
 			},
 		},
-		&credentials.EnvAWS{},
 		&credentials.EnvMinio{},
 		&credentials.FileAWSCredentials{},
 		&credentials.FileMinioClient{},