ci: skip setup-go cache on self-hosted runners (#11985)

* ci: skip setup-go cache on self-hosted runners

The module cache is already local on a persistent self-hosted runner;
archiving ~/go/pkg/mod into cache.tzst at every job's end is pure cost
and can stall (a ~4-minute zstdmt hang was observed on awscli-tests).
runner.environment gates the cache to GitHub-hosted runners only.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* ci: gate the remaining setup-go caches too

The first pass only covered go-version-file steps; go-version steps in
nine workflows (including awscli-tests' own file) kept uploading the
cache archive on self-hosted runners.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

.github/workflows/rust-volume-server-tests.yml

@@ -221,6 +221,7 @@ jobs:
         uses: actions/setup-go@v7
         with:
           go-version-file: 'go.mod'
+          cache: ${{ runner.environment == 'github-hosted' }}
 
       - name: Download test binaries
         uses: actions/download-artifact@v7
@@ -285,6 +286,7 @@ jobs:
         uses: actions/setup-go@v7
         with:
           go-version-file: 'go.mod'
+          cache: ${{ runner.environment == 'github-hosted' }}
 
       - name: Download test binaries
         uses: actions/download-artifact@v7