Avoid DUMMY_CONVERSION env var treated as bool in CI

`DUMMY_CONVERSION: True` is treated as a boolean value in YAML[1]. As a
result, during GitHub CI the environment variable setup during tests is
formatted as `DUMMY_CONVERSION=true`.

The value is used[2] in tests and passed as the `condition` to the
`pytest.mark.skipif`[3] decorator. The `skipif` `condition` can be
either a `bool` or `str`. When it is a `str` (our case, as we use
`os.environ.get()`), it is treated as a condition string[4] by pytest.

Since the condition string is `eval()`ed[5] by pytest, trying to
evaluate `true` results in:

> Failed: Error evaluating 'skipif' condition
>     true
> NameError: name 'true' is not defined

To avoid the implicit conversion to a JSON boolean, or marking the
"True" value as a string literal, use the value `1` instead.

[1]: https://yaml.org/type/bool.html
[2]: 9bb1993e77/tests/isolation_provider/base.py (L25)
[3]: https://docs.pytest.org/en/stable/reference/reference.html#pytest-mark-skipif-ref
[4]: https://docs.pytest.org/en/stable/historical-notes.html#string-conditions
[5]: f75dd87eb7/src/_pytest/skipping.py (L117)

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
   windows:
     runs-on: windows-latest
     env:
-      DUMMY_CONVERSION: True
+      DUMMY_CONVERSION: 1
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
@@ -31,7 +31,7 @@ jobs:
   macOS:
     runs-on: macos-latest
     env:
-      DUMMY_CONVERSION: True
+      DUMMY_CONVERSION: 1
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4