chore!: upgrade to node 18

[sofisl]

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Fixes #<issue_number_goes_here> 🦕

[generated-files-bot]

Warning: This pull request is touching the following templated files:

• .kokoro/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/lint.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/samples-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/system-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node18/test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/samples-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/system-test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node18/test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/release/docs-devsite.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/release/docs.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/release/docs.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/samples-test.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/system-test.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/test.bat - .kokoro files are templated and should be updated in synthtool
• .kokoro/test.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/trampoline_v2.sh - .kokoro files are templated and should be updated in synthtool
• .github/workflows/ci.yaml - .github/workflows/ci.yaml (GitHub Actions) should be updated in synthtool

[sofisl]

The last fields aren't updating in the generator because they're not present in index.json. Looking.