Support toolchain syntax added in go 1.21

Changelog.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- golang: Updates go.mod parser to be compatible with golang v1.21. ([#1304](https://github.com/fossas/fossa-cli/pull/1304))
 - `fossa list-targets`: list-target command supports `--format` option with: `ndjson`, `text`, and `legacy`. ([#1296](https://github.com/fossas/fossa-cli/pull/1296))
 
 ## v3.8.17

src/Strategy/Go/Gomod.hs

@@ -82,6 +82,10 @@ data Statement
     -- of go.mod, refer to: https://go.dev/ref/mod#go-mod-file-retract
     RetractStatement
   | GoVersionStatement Text
+  | -- | we do not care about values associated with
+    -- the toolchain block as they are of no use to us today.
+    -- Refer to: https://go.dev/doc/modules/gomod-ref#toolchain
+    ToolchainStatement Text
   deriving (Eq, Ord, Show)
 
 type PackageName = Text
@@ -218,6 +222,7 @@ gomodParser = do
   where
     statement =
       (singleton <$> goVersionStatement) -- singleton wraps the Parser Statement into a Parser [Statement]
+        <|> (singleton <$> toolChainStatements)
         <|> requireStatements
         <|> replaceStatements
         <|> excludeStatements
@@ -228,6 +233,11 @@ gomodParser = do
     goVersionStatement :: Parser Statement
     goVersionStatement = GoVersionStatement <$ lexeme (chunk "go") <*> goVersion
 
+    -- top-level go version statement
+    -- e.g., toolchain go1.21.1
+    toolChainStatements :: Parser Statement
+    toolChainStatements = ToolchainStatement <$ lexeme (chunk "toolchain") <*> anyToken
+
     -- top-level require statements
     -- e.g.:
     --   require golang.org/x/text v1.0.0

test/Go/testdata/go.mod.edgecases

@@ -5,6 +5,8 @@ module test/package
 
 go 1.12
 
+toolchain go1.21.1
+
 require repo/name/A v1.0.0 // indirect
 
 require (