Bump the golang.org/x/exp dependency and fix a build breakage. (#2088)

* Bump the golang.org/x/exp dependency and fix a build breakage.

---------

Signed-off-by: Dan Lorenc <dlorenc@chainguard.dev>
Signed-off-by: Christopher Phillips <christopher.phillips@anchore.com>
Co-authored-by: Christopher Phillips <christopher.phillips@anchore.com>

.github/actions/bootstrap/action.yaml

@@ -4,7 +4,7 @@ inputs:
   go-version:
     description: "Go version to install"
     required: true
-    default: "1.20.x"
+    default: "1.21.x"
   use-go-cache:
     description: "Restore go cache"
     required: true
@@ -24,7 +24,7 @@ inputs:
 runs:
   using: "composite"
   steps:
-    - uses: actions/setup-go@v3
+    - uses: actions/setup-go@v4
       with:
         go-version: ${{ inputs.go-version }}