[release] .github/workflows: run long tests on any branch

It's important to run them on the release branch.

Change-Id: Id39de85269978b81f6350d0a1f00cb47a154de8e
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/239439
Reviewed-by: Rebecca Stambler <[email protected]>
(cherry picked from commit 8d6cea6)
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/239737

Author: hyangah

.github/workflows/test-long.yml

@@ -13,7 +13,7 @@ jobs:
 
     # Not containing 'SKIP CI' in the commit message AND
     # (Either non-Windows OR triggered on 'push' (if triggered by 'pull_request', github.base_ref is not empty)
-    if: "github.ref == 'refs/heads/master' && github.repository == 'golang/vscode-go' && !contains(github.event.head_commit.message, 'SKIP CI')"
+    if: github.repository == 'golang/vscode-go' && !contains(github.event.head_commit.message, 'SKIP CI')"
     timeout-minutes: 20
     strategy:
       fail-fast: false