Fix grammar typos (#15324)

Author: donbarbos

CONTRIBUTING.md

@@ -134,7 +134,7 @@ there represents a PyPI distribution, and contains the following:
   source distribution.
 * (Rarely) some docs specific to a given type stub package in `README` file.
 
-When a third party stub is added or
+When a third-party stub is added or
 modified, an updated version of the corresponding distribution will be
 automatically uploaded to PyPI within a few hours.
 Each time this happens the least significant
@@ -186,7 +186,7 @@ supported:
   stubs for other reasons than the upstream library shipping with type
   information.
 * `upload` (optional): This field is set to `false` to prevent automatic
-  uploads to PyPI. This should only used in special cases, e.g. when the stubs
+  uploads to PyPI. This should only be used in special cases, e.g. when the stubs
   break the upload.
 * `partial_stub` (optional): This field marks the type stub package as
   [partial](https://peps.python.org/pep-0561/#partial-stub-packages). This is for

stdlib/_typeshed/README.md

@@ -1,6 +1,6 @@
 # Utility types for typeshed
 
-This package and its submodules contains various common types used by
+This package and its submodules contain various common types used by
 typeshed. It can also be used by packages outside typeshed, but beware
 the API stability guarantees below.
 

tests/README.md

@@ -110,7 +110,7 @@ This test compares the stdlib stubs against the objects at runtime. Because of
 this, the output depends on which version of Python and on what kind of system
 it is run.
 As such, if you run this test locally, it may complain about system-specific
-differences (in e.g, `socket`) that the type system cannot capture or our stubtest settings
+differences (in e.g., `socket`) that the type system cannot capture or our stubtest settings
 in CI do not account for. If you run into this issue, consider opening a draft PR and letting CI
 test it automatically (or
 [running the test via Github Actions](https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow#running-a-workflow)

tests/REGRESSION.md

@@ -58,7 +58,7 @@ diagnostics.
 Many test cases also make use of
 [`assert_type`](https://docs.python.org/3.11/library/typing.html#typing.assert_type),
 a function which allows us to test whether a type checker's inferred type of an
-expression is what we'd like it be.
+expression is what we'd like it to be.
 
 Finally, some tests make use of `# type: ignore` comments (in combination with
 mypy's