fix: Fix link to CONTRIBUTING.md in PR template (#1910)

Author: dingsdax

.github/pull_request_template.md

@@ -9,5 +9,5 @@
 
 #### Reminders
 - Add GH Issue ID _&_ Linear ID
-- PR title should use [conventional commit](https://develop.sentry.dev/engineering-practices/commit-messages/#type) style (`feat:`, `fix:`, `ref:`, `chore:`)
-- For external contributors: [CONTRIBUTING.md](../CONTRIBUTING.md), [Sentry SDK development docs](https://develop.sentry.dev/sdk/), [Discord community](https://discord.gg/Ww9hbqr)
+- PR title should use [conventional commit](https://develop.sentry.dev/engineering-practices/commit-messages/#type) style (`feat:`, `fix:`, `ref:`, `meta:`)
+- For external contributors: [CONTRIBUTING.md](https://github.com/getsentry/sentry-php/blob/master/CONTRIBUTING.md), [Sentry SDK development docs](https://develop.sentry.dev/sdk/), [Discord community](https://discord.gg/Ww9hbqr)