ci: set fail-fast to false on tests matrix to prevent platform blind spots (#5153)

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This Pull Request fixes/closes #5152 .

It changes the following:

- Appends the explicit `fail-fast: false` property to the `tests` matrix
strategy block within
[.github/workflows/rust.yml](cci:7://file:///c:/Users/risha/Desktop/boa/.github/workflows/rust.yml:0:0-0:0).
- Enhances developer diagnostic visibility by guaranteeing that every OS
environment (`macos`, `windows`, `ubuntu`, `ubuntu-arm`) successfully
completes its full test suite execution, even if a sibling platform
fails first.
- Prevents GitHub Actions' default behavior from instantly
force-cancelling the entire pipeline, eliminating "platform blind spots"
where developers are unaware of platform-specific regressions.

Author: RishavTiwari25

.github/workflows/rust.yml

@@ -211,6 +211,7 @@ jobs:
     env:
       RUSTUP_WINDOWS_PATH_ADD_BIN: 1
     strategy:
+      fail-fast: false
       matrix:
         include:
           - os: macos-14