.github: Fix the go-apidiff action and use the correct version (#75)

Signed-off-by: timflannagan <[email protected]>

Author: timflannagan

.github/workflows/go-apidiff.yml

@@ -11,4 +11,4 @@ jobs:
     - uses: actions/setup-go@v2
       with:
         go-version: 1.16
-    - uses: joelanford/go-apidiff@master
+    - uses: joelanford/go-apidiff@main