I'm sorry to say this happens from time to time because our code obfuscator gets used by malware authors and the virus signature ends up containing our obfuscator signature. You can consider it a false positive.
If it makes you feel any better, you can use an md5 utility and compute a hash on that DLL. It should match if the DLL has not been modified.
The MD5 hash for RedGate.SQLTest.dll version 18.104.22.168 is f809c4370e7150f2fcfdbdff3b4c8de5