ci: fixing flaky CI (#1302)

This PR will apply the same fix as we did for
`.github/workflows/react.yml` to stablize the CI jobs.

The underlying issue is that electron binary installation is expensive
and would some times flake out. The fix here is to skip the binary setup
for workflows that do not need it.

The reason this is a problem is that we need to do a `workspace ...
install` on contract test installations (as `workspaces focus` does some
funny things to non-prod dependencies that may interfere with building
the contract tests). Unfortunately, in `yarn`, `workspace... install`
does the same thing as `yarn install` (installs all deps).

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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk CI-only change that alters dependency install environment for
contract-test services; main risk is an unexpected package needing
Electron in these jobs.
> 
> **Overview**
> Reduces flakiness in the `server-node` and `shopify-oxygen` GitHub
Actions workflows by setting `ELECTRON_SKIP_BINARY_DOWNLOAD=1` for the
contract-test service `yarn workspace ... install` step.
> 
> This avoids unnecessary Electron binary downloads during CI installs
while keeping the rest of the contract-test build and execution flow
unchanged.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
c320ff7. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: joker23

.github/workflows/server-node.yml

@@ -32,6 +32,8 @@ jobs:
           workspace_name: '@launchdarkly/node-server-sdk'
           workspace_path: packages/sdk/server-node
       - name: Install contract test service dependencies
+        env:
+          ELECTRON_SKIP_BINARY_DOWNLOAD: '1'
         run: yarn workspace @launchdarkly/node-server-sdk-contract-tests install --no-immutable
       - name: Build shared contract test utils (server)
         run: yarn workspace @launchdarkly/js-contract-test-utils build:server

.github/workflows/shopify-oxygen.yml

@@ -27,6 +27,8 @@ jobs:
           workspace_name: '@launchdarkly/shopify-oxygen-sdk'
           workspace_path: packages/sdk/shopify-oxygen
       - name: Install contract test service dependencies
+        env:
+          ELECTRON_SKIP_BINARY_DOWNLOAD: '1'
         run: yarn workspace @launchdarkly/shopify-oxygen-contract-tests install --no-immutable
       - name: Build shared contract test utils
         run: yarn workspace @launchdarkly/js-contract-test-utils build:server