Unnecessary dependency on importlib_metadata in Python 3.8+

[nchepanov]

Describe the bug
The package declares an install_requires dependency on importlib_metadata >= 3.6, this however is not necessary for Python 3.8+: https://docs.python.org/3.8/library/importlib.metadata.html#

Proposal

Change the package setup.py to not require importlib_metadata in Python 3.8+ and use conditional imports.

Please let me know if you'd like a PR

diff --git a/hook-keyring.backend.py b/hook-keyring.backend.py
index 16d4044..c453f21 100644
--- a/hook-keyring.backend.py
+++ b/hook-keyring.backend.py
@@ -1,6 +1,9 @@
 # Used by pyinstaller to expose hidden imports

-import importlib_metadata as metadata
+try:
+    import importlib.metadata as metadata
+except ImportError:
+    import importlib_metadata as metadata


 hiddenimports = [ep.value for ep in metadata.entry_points(group='keyring.backends')]
diff --git a/keyring/backend.py b/keyring/backend.py
index ee6b256..3041faf 100644
--- a/keyring/backend.py
+++ b/keyring/backend.py
@@ -9,7 +9,11 @@ import operator

 from typing import Optional

-import importlib_metadata as metadata
+try:
+    import importlib.metadata as metadata
+except ImportError:
+    import importlib_metadata as metadata
+

 from . import credentials, errors, util
 from .util import properties
diff --git a/setup.cfg b/setup.cfg
index aa82e2e..54e2ec6 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -25,7 +25,7 @@ install_requires =
        pywin32-ctypes!=0.1.0,!=0.1.1; sys_platform=="win32"
        SecretStorage>=3.2; sys_platform=="linux"
        jeepney>=0.4.2; sys_platform=="linux"
-       importlib_metadata >= 3.6
+       importlib_metadata >= 3.6; python_version < "3.8"
 setup_requires = setuptools_scm[toml] >= 3.4.1

 [options.packages.find]

[mitya57]

Please look at closed issues, this was already discussed several times.

Keyring is using the new API which is not available in Python 3.8 or 3.9, see #503 (comment) for details.