Update continuous integration system

This PR updates the CI system to the standardized GitHub Actions-based CI configuration for Arduino libraries.

Dependabot

Dependabot will periodically check the versions of all actions used in the repository's workflows. If any are found to be outdated, it will submit a pull request to update them.

NOTE: Dependabot's PRs will sometimes try to pin to the patch version of the action (e.g., updating uses: foo/bar@v1 to uses: foo/bar@v2.3.4). When the action author has provided a major version ref, use that instead (e.g., uses: foo/bar@v2). Once the major version has been updated in the workflow, Dependabot should not submit an update PR again until the next major version bump. So even if the PRs from Dependabot are not always exactly correct, their value lies in bringing the maintainer's attention to the fact that the action version in use is outdated. Dependabot will automatically close its PR once the workflow has been updated.

More information: https://docs.github.com/en/github/administering-a-repository/keeping-your-actions-up-to-date-with-dependabot

Spell check

On every push, pull request, and periodically, use the codespell-project/actions-codespell action to check for commonly misspelled words.

In the event of a false positive, the problematic word should be added, in all lowercase, to the ignore-words-list field of ./.codespellrc. Regardless of the case of the word in the false positive, it must be in all lowercase in the ignore list. The ignore list is comma-separated with no spaces.

Arduino Lint

On every push, pull request, and periodically, run Arduino Lint to check for common problems not related to the project code.

Compile examples

On every push or pull request that affects library source or example files, and periodically, use the arduino/compile-sketches action to compile all example sketches for the specified boards.

Report size deltas

On creation or commit to a pull request, use the arduino/report-size-deltas action to comment a report of the resulting change in memory usage of the examples to the PR thread.

Fixes https://github.com/arduino-libraries/ArduinoBearSSL/issues/47

Memory usage change @ 72be849120c892a4b253f197a492a945a5a642ef

Board	flash	%	RAM for global variables	%
arduino:megaavr:uno2018	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkr1000	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrgsm1400	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board|examples/SHA1
flash|%|examples/SHA1
RAM for global variables|%|examples/SHA256
flash|%|examples/SHA256
RAM for global variables|%|examples/WiFiSSLClient
flash|%|examples/WiFiSSLClient
RAM for global variables|%|examples/MKRGSMSSLClient
flash|%|examples/MKRGSMSSLClient
RAM for global variables|% -|-|-|-|-|-|-|-|-|-|-|-|-|-|-|-|- arduino:megaavr:uno2018|0|0.0|0|0.0|0|0.0|0|0.0 arduino:samd:mkr1000|0|0.0|0|0.0|0|0.0|0|0.0|0|0.0|0|0.0 arduino:samd:mkrgsm1400|0|0.0|0|0.0|0|0.0|0|0.0|||||0|0.0|0|0.0

Click for full report CSV

``` Board,examples/SHA1
flash,%,examples/SHA1
RAM for global variables,%,examples/SHA256
flash,%,examples/SHA256
RAM for global variables,%,examples/WiFiSSLClient
flash,%,examples/WiFiSSLClient
RAM for global variables,%,examples/MKRGSMSSLClient
flash,%,examples/MKRGSMSSLClient
RAM for global variables,% arduino:megaavr:uno2018,0,0.0,0,0.0,0,0.0,0,0.0 arduino:samd:mkr1000,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0 arduino:samd:mkrgsm1400,0,0.0,0,0.0,0,0.0,0,0.0,,,,,0,0.0,0,0.0 ```

arduino-libraries / ArduinoBearSSL