utils/analytics: improve accuracy of GitHub Packages download counts

`millions_match.captures.first` will typically be a decimal (since it's
matched using `\d+\.\d+`), except we lose accuracy in the `#to_i`
conversion.

Before:
```
❯ brew info --analytics --github-packages-downloads sqlite
==> Analytics
==> install (30 days)
[snip]
==> GitHub Packages Downloads
1,009,898 (30 days)
```

After:

```
❯ brew info --analytics --github-packages-downloads sqlite
==> Analytics
==> install (30 days)
[snip]
==> GitHub Packages Downloads
1,199,898 (30 days)
```

In this case `1.19M` was being rounded down to `1M`.

Library/Homebrew/utils/analytics.rb

@@ -307,7 +307,7 @@ def output_github_packages_downloads(formula, args:)
 
           last_thirty_days_downloads = last_thirty_days_match.captures.first.tr(",", "")
           thirty_day_download_count += if (millions_match = last_thirty_days_downloads.match(/(\d+\.\d+)M/).presence)
-            millions_match.captures.first.to_i * 1_000_000
+            millions_match.captures.first.to_f * 1_000_000
           else
             last_thirty_days_downloads.to_i
           end