Fix PDF status button in Gravity Forms 2.8.8+

[jakejackson1]

Description

Fixes #1520

Testing instructions

1. Install Gravity Forms 2.8.7
2. View PDF List page and toggle status button
3. Install Gravity Forms 2.8.8
4. View PDF List page and toggle status button

Checklist:

• [x] I've tested the code.
• [x] My code is easy to read, follow, and understand
• [ ] My code follows the accessibility standards.
• [x] My code has proper inline documentation / docblocks.

Additional Comments

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 76.13%. Comparing base (24eacd5) to head (834c767). Report is 1 commits behind head on development.

Files	Patch %	Lines
src/Helper/Helper_PDF_List_Table.php	66.66%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## development #1524 +/- ## =============================================== - Coverage 76.14% 76.13% -0.01% =============================================== Files 248 248 Lines 12918 12922 +4 Branches 370 370 =============================================== + Hits 9836 9838 +2 - Misses 3074 3076 +2 Partials 8 8 ```

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