Fix build with QuickCheck 2.10.

QuickCheck added an Arbitrary instance for CTime aka EpochTime. However,
while git-annex's instance disallowed times before the epoch, QuickCheck's
does not. So, rather than using its instance, convert from an Integer.

This commit was sponsored by Thomas Hochstein on Patreon.

Utility/InodeCache.hs

@@ -210,7 +210,8 @@ instance Arbitrary InodeCache where
 		let prim = InodeCachePrim
 			<$> arbitrary
 			<*> arbitrary
-			<*> arbitrary
+			-- timestamp cannot be negative
+			<*> (abs . fromInteger <$> arbitrary)
 		in InodeCache <$> prim
 
 #ifdef mingw32_HOST_OS