chore: bump actions/cache from 4 to 6

Bumps [actions/cache](https://github.com/actions/cache) from 4 to 6.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](https://github.com/actions/cache/compare/v4...v6)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/build_and_test_elixir.yml

diff --git a/.github/workflows/build_and_test_elixir.yml b/.github/workflows/build_and_test_elixir.yml
index 922b447..a7c94de 100644
--- a/.github/workflows/build_and_test_elixir.yml
+++ b/.github/workflows/build_and_test_elixir.yml
@@ -66,7 +66,7 @@
         uses: Swatinem/rust-cache@c19371144df3bb44fab255c43d04cbc2ab54d1c4 # v2.9.1
 
       - name: Cache Mix deps and build
-        uses: actions/cache@v4
+        uses: actions/cache@v6
         with:
           path: |
             bindings/elixir/deps
@@ -95,7 +95,7 @@
         run: mix credo
 
       - name: Cache PLT
-        uses: actions/cache@v4
+        uses: actions/cache@v6
         with:
           path: bindings/elixir/priv/plts/
           key: ${{ runner.os }}-otp-${{ steps.beam.outputs.otp-version }}-elixir-${{ steps.beam.outputs.elixir-version }}-mix-${{ hashFiles('bindings/elixir/mix.lock') }}-plt