False positive: `ItsPossessive` flags `it's` heading a complement clause ("I have heard it's good news")

**What got flagged?**

`ItsPossessive` flags `it's` in "I have heard it's good news."

```
harper-cli lint "I have heard it's good news."

1 │ I have heard it's good news.
│ ──┬─
│ ╰─── [Agreement::ItsPossessive] (pri 31): Use the possessive
│ pronoun `its` (without an apostrophe) to show ownership.
```

**Why is this incorrect?**

Here `it's` genuinely means "it is". The sentence is "I have heard \[that\] it is good news." Rewriting it to `its` produces "I have heard its good news.", which changes the meaning.

The `mid_sentence` expression in `harper-core/src/linting/its_possessive.rs` matches `VERB`/`ADP` + `it's` + optional `ADJ` + `NOUN`. In this sentence "heard" is the `VERB`, "good" the `ADJ` and "news" the `NOUN`, so the pattern matches even though `it's` is heading a complement clause rather than modifying "news".

**Example of correct usage:**

* "I have heard it's good news."
* "They said it's bad weather today."

Contrast with the true positives the rule is aimed at, which still work correctly:

* "The engine lost it's compression." -> should be `its`
* "I admired the sculpture for it's intricacy." -> should be `its`

**Notes**

Found while working on Automattic/harper#3627 / [#4035](). This reproduces on `master` and is not caused by that change, which only affects a preceding `has`/`had`.

Start by reading harper-core/src/linting/its_possessive.rs, especially the mid_sentence expression, and reproduce the report with harper-cli lint "I have heard it's good news.". Done means the complement-clause example is no longer flagged while the listed possessive examples still produce the intended result.

Written by the indexing model from the issue text.