docs: fix typo in pipelineruns.md

Correct the type name from `PipelineRunTaskSpec` to `PipelineTaskRunSpec` in
taskRunSpecs field description.

Author: l-qing

docs/pipelineruns.md

@@ -73,7 +73,7 @@ A `PipelineRun` definition supports the following fields:
   - [`serviceAccountName`](#specifying-custom-serviceaccount-credentials) - Specifies a `ServiceAccount`
     object that supplies specific execution credentials for the `Pipeline`.
   - [`status`](#cancelling-a-pipelinerun) - Specifies options for cancelling a `PipelineRun`.
-  - [`taskRunSpecs`](#specifying-taskrunspecs) - Specifies a list of `PipelineRunTaskSpec` which allows for setting `ServiceAccountName`, [`Pod` template](./podtemplates.md), and `Metadata` for each task. This overrides the `Pod` template set for the entire `Pipeline`.
+  - [`taskRunSpecs`](#specifying-taskrunspecs) - Specifies a list of `PipelineTaskRunSpec` which allows for setting `ServiceAccountName`, [`Pod` template](./podtemplates.md), and `Metadata` for each task. This overrides the `Pod` template set for the entire `Pipeline`.
   - [`timeout`](#configuring-a-failure-timeout) - Specifies the timeout before the `PipelineRun` fails. `timeout` is deprecated and will eventually be removed, so consider using `timeouts` instead.
   - [`timeouts`](#configuring-a-failure-timeout) - Specifies the timeout before the `PipelineRun` fails. `timeouts` allows more granular timeout configuration, at the pipeline, tasks, and finally levels
   - [`podTemplate`](#specifying-a-pod-template) - Specifies a [`Pod` template](./podtemplates.md) to use as the basis for the configuration of the `Pod` that executes each `Task`.