build: tidy after go mod edit

To ensure the `go.sum` is always up-to-date when the following `go mod
edit` is executed.

Signed-off-by: Hidde Beydals <hello@hidde.co>

.github/workflows/update.yaml

@@ -42,6 +42,8 @@ jobs:
 
             if [[ "${MOD_VERSION}" != "${LATEST_VERSION}" ]]; then
               go mod edit -require="github.com/fluxcd/$1/api@${LATEST_VERSION}"
+              rm go.sum
+              go mod tidy
               changed=true
             fi
 
@@ -59,9 +61,6 @@ jobs:
             bump_version image-reflector-controller
             bump_version image-automation-controller
 
-            # add missing and remove unused modules
-            go mod tidy
-
             # diff change
             git diff