Run tests and rule validation in CI

[NicholasEllul]

Summary

This pull request adds a GitHub workflow that will run Semgrep rule validation and Semgrep tests in CI. This will help ensure the rules we are developing are vetted prior to merge.

Testing

1. Make an adjustment to one of the existing rules in the rules/src/ directory that breaks the config file in some way (e.g rename pattern to patern)
2. Run bin/validate-rules and see that it gets flagged.

Example output

/src/metamask/semgrep-action (ellul/ci-checks) » bin/validate-rules                         
Configuration is invalid - found 2 configuration error(s), and 0 rule(s).
semgrep error: Invalid rule schema
  --> rules/src/github-actions/publish-actions-cache-used.yml:11
11 |       - patterns:
12 |           - patern: "uses: $ACTION_NAME"
13 |           - metavariable-regex:
14 |               metavariable: $ACTION_NAME
15 |               regex: actions/cache@v[0-9]+
16 |     paths:

Additional properties are not allowed ('patterns' was unexpected)

[ERROR] Rule parse error in rule publish-actions-cache-used:
 unexpected key patern

3. Correct the rule you broke above, and modify one of the files in the rules/test directory such that one of the lines flagging a rule (which look like --> ruleid: publish-actions-cache-used), is renamed to # ok: publish-actions-cache-used.
4. See that Semgrep warns you that a test did not pass.

Example output

~/src/metamask/semgrep-action (ellul/ci-checks*) » bin/test                             
0/1: 1 unit tests did not pass:
--------------------------------------------------------------------------------
        ✖ publish-actions-cache-used
        missed lines: [], incorrect lines: [89]
        test file path: /Users/ellul/src/metamask/semgrep-action/rules/test/github-actions/publish-actions-cache-used.test.yaml


No tests for fixes found.