[2.9.2] Convert to Blocks not properly converting successive Shortcodes

[GlennMartin1]

Describe the bug
On a Classic block with multiple successive Shortcodes, choose the option "Convert to Blocks." Not all the Shortcodes will convert.

To Reproduce
Steps to reproduce the behavior:

1. create a new page/post
2. add this content in a Classic block
   [shortcodetest]
   [shortcodetest]
   [shortcodetest]
3. choose "Convert to Blocks"
4. BUG: It will not create all the Shortcode blocks

Different combinations of text with successive Shortcodes result in different behavior, but in most/all scenarios, at least one of multiple successive Shortcodes does not convert.

Expected behavior
Any combination of Shortcodes, even in succession, should convert to Shortcode blocks.

[danielbachhuber]

I've confirmed this bug:

In my testing, it's the last shortcode that isn't converted to a block.

[danielbachhuber]

I suspect this is going to be a more common issue than not, so elevating priority.

Related #3900 #4456

[danielbachhuber]

Interestingly, opening a post in the Classic Editor immediately wraps shortcodes with paragraph tags:

Related #3900