actions: keep lockfile generator go.mod free of local replace

The previous commit re-staged a dirty working-tree go.mod, so the
machine-specific replace directive pointing at a local actions-lockfile
clone leaked back into the tree. Drop it for real and move the local
replace into a gitignored go.work so committed module metadata stays
portable while local builds still resolve the not-yet-public dependency.

Author: nodeselector

actions/extractor/tools/lockfile-extension-generator/.gitignore

@@ -1 +1,5 @@
 /lockfile-extension-generator
+
+# local-only module workspace carrying the actions-lockfile replace
+go.work
+go.work.sum

actions/extractor/tools/lockfile-extension-generator/go.mod

@@ -13,5 +13,3 @@ require gopkg.in/yaml.v3 v3.0.1 // indirect
 //   go mod edit -replace github.com/github/actions-lockfile/go=/path/to/actions-lockfile/go
 //
 // Remove this replace directive once actions-lockfile is published.
-
-replace github.com/github/actions-lockfile/go => /Users/nodeselector/ghq/github.com/github/actions-lockfile/go