chore: run test-go-pg on macOS and Windows in regular CI (#17853)

This PR starts running test-go-pg on macOS and Windows in regular CI.
Previously this suite was only run in the nightly gauntlet for 2
reasons:

- it was flaky
- it was slow (took 17 minutes)

We've since stabilized the flakiness by switching to depot runners,
using ram disks, optimizing the number of tests run in parallel, and
automatically re-running failing tests. We've also [brought
down](https://github.com/coder/coder/pull/17756) the time to run the
suite to 9 minutes. Additionally, this PR allows test-go-pg to use cache
from previous runs, which speeds it up further. The cache is only used
on PRs, `main` will still run tests without it.

This PR also:

- removes the nightly gauntlet since all tests now run in regular CI
- removes the `test-cli` job for the same reason
- removes the `setup-imdisk` action which is now fully replaced by
[coder/setup-ramdisk-action](https://github.com/coder/setup-ramdisk-action)
- makes 2 minor changes which could be separate PRs, but I rolled them
into this because they were helpful when iterating on it:
- replace the `if: always()` condition on the `gen` job with a `if: ${{
!cancelled() }}` to allow the job to be cancelled. Previously the job
would run to completion even if the entire workflow was cancelled. See
[the GitHub
docs](https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/evaluate-expressions-in-workflows-and-actions#always)
for more details.
- disable the recently added `TestReinitializeAgent` since it does not
pass on Windows with Postgres. There's an open issue to fix it:
https://github.com/coder/internal/issues/642

This PR will:

- unblock https://github.com/coder/coder/issues/15109
- alleviate https://github.com/coder/internal/issues/647

I tested caching by temporarily enabling cache upload on this PR: here's
[a
run](https://github.com/coder/coder/actions/runs/15119046903/job/42496939341?pr=17853#step:13:1296)
showing cache being used.

.github/actions/setup-go-paths/action.yml

@@ -0,0 +1,57 @@
+name: "Setup Go Paths"
+description: Overrides Go paths like GOCACHE and GOMODCACHE to use temporary directories.
+outputs:
+  gocache:
+    description: "Value of GOCACHE"
+    value: ${{ steps.paths.outputs.gocache }}
+  gomodcache:
+    description: "Value of GOMODCACHE"
+    value: ${{ steps.paths.outputs.gomodcache }}
+  gopath:
+    description: "Value of GOPATH"
+    value: ${{ steps.paths.outputs.gopath }}
+  gotmp:
+    description: "Value of GOTMPDIR"
+    value: ${{ steps.paths.outputs.gotmp }}
+  cached-dirs:
+    description: "Go directories that should be cached between CI runs"
+    value: ${{ steps.paths.outputs.cached-dirs }}
+runs:
+  using: "composite"
+  steps:
+    - name: Override Go paths
+      id: paths
+      uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7
+      with:
+        script: |
+          const path = require('path');
+
+          // RUNNER_TEMP should be backed by a RAM disk on Windows if
+          // coder/setup-ramdisk-action was used
+          const runnerTemp = process.env.RUNNER_TEMP;
+          const gocacheDir = path.join(runnerTemp, 'go-cache');
+          const gomodcacheDir = path.join(runnerTemp, 'go-mod-cache');
+          const gopathDir = path.join(runnerTemp, 'go-path');
+          const gotmpDir = path.join(runnerTemp, 'go-tmp');
+
+          core.exportVariable('GOCACHE', gocacheDir);
+          core.exportVariable('GOMODCACHE', gomodcacheDir);
+          core.exportVariable('GOPATH', gopathDir);
+          core.exportVariable('GOTMPDIR', gotmpDir);
+
+          core.setOutput('gocache', gocacheDir);
+          core.setOutput('gomodcache', gomodcacheDir);
+          core.setOutput('gopath', gopathDir);
+          core.setOutput('gotmp', gotmpDir);
+
+          const cachedDirs = `${gocacheDir}\n${gomodcacheDir}`;
+          core.setOutput('cached-dirs', cachedDirs);
+
+    - name: Create directories
+      shell: bash
+      run: |
+        set -e
+        mkdir -p "$GOCACHE"
+        mkdir -p "$GOMODCACHE"
+        mkdir -p "$GOPATH"
+        mkdir -p "$GOTMPDIR"