fix(civil): add replace directive for civil module in spanner test

Fixes the vet.sh failure after civil was extracted into its own module.
The spanner test module replaced the root cloud.google.com/go with a
local path, but that path no longer contains the civil package.

Author: monstermunchkin

spanner/test/opentelemetry/test/go.mod

@@ -4,6 +4,7 @@ go 1.25.8
 
 replace (
 	cloud.google.com/go => ../../../../
+	cloud.google.com/go/civil => ../../../../civil
 	cloud.google.com/go/spanner => ../../..
 )
 
@@ -23,6 +24,7 @@ require (
 	cloud.google.com/go v0.123.0 // indirect
 	cloud.google.com/go/auth v0.20.0 // indirect
 	cloud.google.com/go/auth/oauth2adapt v0.2.8 // indirect
+	cloud.google.com/go/civil v0.0.0-00010101000000-000000000000 // indirect
 	cloud.google.com/go/compute/metadata v0.9.0 // indirect
 	cloud.google.com/go/iam v1.11.0 // indirect
 	cloud.google.com/go/longrunning v1.0.0 // indirect