ci: move testing with MySQL to a new workflow

Integration tests with MySQL are working locally but not in the GitHub
Runner. We don't know yet why. See:

#580

That's affecting deployments and releases. We move the execution to a
new temporary workflows until it's fixed. Be sure to execute it locally
before opening new PR:

```console
./contrib/dev-tools/container/e2e/mysql/run-e2e-tests.sh
```

Author: josecelano

.github/workflows/e2e.yaml

@@ -0,0 +1,44 @@
+# Temporary execution of E2E tests using MySQL becuase it's failing
+# in the `testing.yml` workflows and affects deployments and releases.
+# See https://github.com/torrust/torrust-index/issues/580
+name: E2E Testing
+
+on:
+  push:
+  pull_request:
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  e2e:
+    name: E2E
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        toolchain: [stable, nightly]
+
+    steps:
+      - id: checkout
+        name: Checkout Repository
+        uses: actions/checkout@v4
+
+      - id: setup
+        name: Setup Toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ matrix.toolchain }}
+
+      - id: cache
+        name: Enable Job Cache
+        uses: Swatinem/rust-cache@v2
+
+      # Temporary Cleaning to avoid Rust Compiler Bug
+      - id: clean
+        name: Make Build Clean
+        run: cargo clean
+
+      - id: test-mysql
+        name: Run Integration Tests (MySQL)
+        run: ./contrib/dev-tools/container/e2e/mysql/run-e2e-tests.sh

.github/workflows/testing.yaml

@@ -156,6 +156,6 @@ jobs:
         name: Run Integration Tests (SQLite)
         run: ./contrib/dev-tools/container/e2e/sqlite/run-e2e-tests.sh
 
-      - id: test-mysql
-        name: Run Integration Tests (MySQL)
-        run: ./contrib/dev-tools/container/e2e/mysql/run-e2e-tests.sh
+      #- id: test-mysql
+      #  name: Run Integration Tests (MySQL)
+      #  run: ./contrib/dev-tools/container/e2e/mysql/run-e2e-tests.sh