Use T.isInfixOf as equality check for doc string

Follows @fendor's suggestion to ignore some details in the doc string.

Author: jian-lin

haskell-language-server.cabal

@@ -882,9 +882,9 @@ test-suite hls-signature-help-plugin-tests
     , hls-test-utils             == 2.11.0.0
     , lens
     , lsp-types
-    , regex-tdfa
     , text
   default-extensions:
+    DerivingStrategies
     OverloadedStrings
 
 -----------------------------