cmd/syncthing: Fix help text for STRECHECKDBEVERY (fixes #4764)

cmd/syncthing/main.go

@@ -197,7 +197,7 @@ are mostly useful for developers. Use with care.
                    "minio" for the github.com/minio/sha256-simd implementation,
                    and blank (the default) for auto detection.
 
- STDBCHECKEVERY    Set to a time interval to override the default database
+ STRECHECKDBEVERY  Set to a time interval to override the default database
                    check interval of 30 days (720h). The interval understands
                    "h", "m" and "s" abbreviations for hours minutes and seconds.
                    Valid values are like "720h", "30s", etc.