Pin python 3.7 patch to 3.7.16

[jcscottiii]

This is an attempt at a workaround for #40525

[jcscottiii]

windows only has the following versions:

Version spec 3.7.16 for architecture x64 did not match any version in Agent.ToolsDirectory.
Versions in C:\hostedtoolcache\windows:
3.10.11 (x86)
3.11.4 (x86)
3.6.8 (x86)
3.7.9 (x86)
3.8.10 (x86)
3.9.13 (x86)
3.10.11 (x64)
3.11.4 (x64)
3.6.8 (x64)
3.7.9 (x64)
3.8.10 (x64)
3.9.13 (x64)

Will just leave that pinned at the minor level

(Tried to pin windows at the same patch version as mac for consistency. But it seems like that is not an option.)

[jcscottiii]

It worked. https://github.com/web-platform-tests/wpt/pull/40526/checks?check_run_id=14233986094

[jcscottiii]

This is ready to go

[gsnedders]

@jcscottiii can you also comment on the upstream issue that the older Python isn't affected, even on the current image?

[jcscottiii]

Done!