Remove spacetimedb-update test on aarch64 (#5348)

# Description of Changes

<!-- Please describe your change, mention any related tickets, and so on
here. -->

This removes the `spacetimedb-update` check specifically on arm. This
test doesn't have a whole lot of value because we're already covering
Linux + Windows on x86 and then macOS on aarch64. Removing this will
allow us to decom the arm runner.

# API and ABI breaking changes

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corresponding GitHub label. -->

None - just a CI change

# Expected complexity level and risk

1

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# Testing

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reviewers to do,
so that you're confident that all the changes work as expected! -->

- I have not tested this but me and Zeke sync'd on this and we think it
makes sense.

.github/workflows/ci.yml

@@ -462,7 +462,6 @@ jobs:
       matrix:
         include:
           - { target: x86_64-unknown-linux-gnu, runner: spacetimedb-new-runner-2 }
-          - { target: aarch64-unknown-linux-gnu, runner: arm-runner }
           - { target: aarch64-apple-darwin, runner: macos-latest }
           - { target: x86_64-pc-windows-msvc, runner: windows-latest }
     runs-on: ${{ matrix.runner }}
@@ -480,11 +479,6 @@ jobs:
       - name: Install rust target
         run: rustup target add ${{ matrix.target }}
 
-      - name: Install packages
-        if: ${{ matrix.runner == 'arm-runner' }}
-        shell: bash
-        run: sudo apt install -y libssl-dev
-
       - name: Test spacetimedb-update
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}