ADR 10: Replace <= with ≤ to avoid linting errors

[matevz]

Docusaurus 3.0.1 MDX linter complains:

Error: MDX compilation failed for file "/home/oa/docs/docs/adrs/0010-vrf-elections.md"
Cause: Unexpected character `=` (U+003D) before name, expected a character that can start a name, such as a letter, `$`, or `_`
Details:
{
  "column": 23,
  "message": "Unexpected character `=` (U+003D) before name, expected a character that can start a name, such as a letter, `$`, or `_`",
  "line": 39,
  "name": "39:23",
  "place": {
    "line": 39,
    "column": 23,
    "offset": 1093,
    "_index": 2,
    "_bufferIndex": 20
  },
  "reason": "Unexpected character `=` (U+003D) before name, expected a character that can start a name, such as a letter, `$`, or `_`",
  "ruleId": "unexpected-character",
  "source": "micromark-extension-mdx-jsx",
  "url": "https://github.com/micromark/micromark-extension-mdx-jsx#unexpected-character-at-expected-expect"
}
error Command failed with exit code 1.

Replacing <= with ≤ or ≤ seems to fix it.