b2/s3: Move config validation from ApplyEnvironment to Open/Create

Conceptually the backend configuration should be validated when creating
or opening the backend, but not when filling in information from
environment variables into the configuration.

internal/backend/swift/config.go

@@ -77,7 +77,7 @@ func ParseConfig(s string) (*Config, error) {
 var _ restic.ApplyEnvironmenter = &Config{}
 
 // ApplyEnvironment saves values from the environment to the config.
-func (cfg *Config) ApplyEnvironment(prefix string) error {
+func (cfg *Config) ApplyEnvironment(prefix string) {
 	for _, val := range []struct {
 		s   *string
 		env string
@@ -130,5 +130,4 @@ func (cfg *Config) ApplyEnvironment(prefix string) error {
 			*val.s = options.NewSecretString(os.Getenv(val.env))
 		}
 	}
-	return nil
 }

internal/backend/swift/swift_test.go

@@ -48,9 +48,7 @@ func newSwiftTestSuite(t testing.TB) *test.Suite[swift.Config] {
 				return nil, err
 			}
 
-			if err = cfg.ApplyEnvironment("RESTIC_TEST_"); err != nil {
-				return nil, err
-			}
+			cfg.ApplyEnvironment("RESTIC_TEST_")
 			cfg.Prefix += fmt.Sprintf("/test-%d", time.Now().UnixNano())
 			t.Logf("using prefix %v", cfg.Prefix)
 			return cfg, nil