Use stable go version in gh actions (#6530)

Setup-go has some non-straitforward tricks:

https://github.com/actions/setup-go?tab=readme-ov-file#getting-go-version-from-the-gomod-file
> The go directive in go.mod can specify a patch version or omit it
altogether (e.g., go 1.22.0 or go 1.22).
If a patch version is specified, that specific patch version will be
used.
If no patch version is specified, it will search for the latest
available patch version in the cache,
[versions-manifest.json](https://github.com/actions/go-versions/blob/main/versions-manifest.json),
and the [official Go language
website](https://golang.org/dl/?mode=json&include=all), in that order.

This is an invention of setup-go action authors. Go team
[says](golang/go#68971 (comment))
that release version (e.g. 1.22.0) should be specified

That means, e.g. when [this
commit](8f46514#diff-33ef32bf6c23acb95f5902d7097b7a1d5128ca061167ec0716715b0b9eeaa5f6R3)
updated go.mod from 1.22 to 1.22.0, the "Long JetStream tests" silently
started to use 1.22.0, instead of 1.22.12.
"If nothing magically works, nothing magically breaks".

Since we update to the new toolchain version as soon as it is released,
and we usually use the latest toolchain for the releases, we should run
all tests using [go-version:
stable](https://github.com/actions/setup-go?tab=readme-ov-file#using-stableoldstable-aliases)


Signed-off-by: Alex Bozhenko <[email protected]>

Author: derekcollison

Diff for: .github/actions/nightly-release/action.yaml

@@ -22,9 +22,9 @@ runs:
       run: docker login -u "${{ inputs.hub_username }}" -p "${{ inputs.hub_password }}"
 
     - name: Set up Go
-      uses: actions/setup-go@v4
+      uses: actions/setup-go@v5
       with:
-        go-version: "stable"
+        go-version: stable
 
     - name: Build and push Docker images
       # Use commit hash here to avoid a re-tagging attack, as this is a third-party action

Diff for: .github/workflows/cov.yaml

@@ -22,7 +22,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version-file: src/github.com/nats-io/nats-server/go.mod
+          go-version: stable
           cache-dependency-path: src/github.com/nats-io/nats-server/go.sum
 
       - name: Run code coverage

Diff for: .github/workflows/long-tests.yaml

@@ -24,10 +24,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@v5
         with:
-          # Use go version from go.mod
-          go-version-file: "go.mod"
-          # Use latest stable go version
-          # go-version: stable
+          go-version: stable
 
       - name: Run tests
         run: go test -race -v -run='^TestLong.*' ./server -tags=include_js_long_tests -count=1 -vet=off -timeout=60m -shuffle on -p 1 -failfast

Diff for: .github/workflows/mqtt-test.yaml

@@ -16,7 +16,7 @@ jobs:
       - name: Setup Go
         uses: actions/setup-go@v5
         with:
-          go-version-file: src/github.com/nats-io/nats-server/go.mod
+          go-version: stable
           cache-dependency-path: src/github.com/nats-io/nats-server/go.sum
 
       - name: Set up testing tools and environment