Bug 1717051: Spell `glean-sdk` with a dash, not an underscore r=ahal

The Glean SDK was traditionally represented in-tree as `glean_sdk`.
However, on PyPI and in `pip list`, it appears as `glean-sdk` (`pip` was
doing the translation implicitly and internally).

This is breaking our virtualenv state-checking code, since it thinks
that `glean_sdk` isn't installed.

Since `glean_sdk` was marked as `pypi-optional`, this hasn't affected us
yet, but it will when we bump the Glean SDK version, because developers'
virtualenvs won't be detected as out-of-date.

Differential Revision: https://phabricator.services.mozilla.com/D122500

build/mach_virtualenv_packages.txt

@@ -1,7 +1,7 @@
 packages.txt:build/common_virtualenv_packages.txt
-# glean_sdk may not be installable if a wheel isn't available
+# glean-sdk may not be installable if a wheel isn't available
 # and it has to be built from source.
-pypi-optional:glean_sdk==36.0.0:telemetry will not be collected
+pypi-optional:glean-sdk==36.0.0:telemetry will not be collected
 # Mach gracefully handles the case where `psutil` is unavailable.
 pypi-optional:psutil==5.8.0:telemetry will be missing some data
-pypi:zstandard==0.15.2
+pypi:zstandard==0.15.2