Update askama requirement from 0.7.2 to 0.9.0

[dependabot-preview]

Updates the requirements on askama to permit the latest version.

Release notes

Sourced from askama's releases.

0.9.0

After 11 months of development, I'm happy to announce the availability of version 0.8 of Askama, the type-safe, compiled Jinja-like template engine for Rust. This has been a long release cycle; mostly I've spent quite a bit of time trying to figure out problems with how to manage Askama's built-in integrations. In the end, 0.9.0 shipped with the integrations problems unsolved, but they were solved shortly thereafter.

Upgrade notes:

• Move no-receiver size_hint() method to a separate trait (#270, thanks to @jbg)
• Upgrade Actix-Web integration to Actix-Web 2.0 (#286, thanks to @DCjanus)
• Default Actix-Web and Gotham integrations to UTF-8 (#219, thanks to @spease)

Other changes:

• Add basic support for {% raw %} blocks (#231, thanks to @fokinpv)
• Allow referencing self as a variable (fixes #207)
• Add support for boolean literals (#265, thanks to @davebrent)
• Add support for character literals (#283, thanks to @siiptuo)
• Support escaping in string literals (#287, thanks to @siiptuo)
• Improve interface for askama_escape (#243, thanks to @quadrupleslap)
• Allow Rust macro calls in more places (#226)
• Fix a regression in partial inheritance (#224)
• Improvements to the Actix-Web integration (#223, thanks to @DoumanAsh)
• Clarify documentation on filter precedence (#230, thanks to @notsimon)
• Add documentation on how to deal with recursive data types (#235, thanks to @drahnr)
• Add documentation on nesting Template types (#218, thanks to @victe)
• Improve documentation for Actix-Web and Gotham integrations (#250, thanks to @bardiharborow)
• Upgrade to nom 5 and non-macro parser combinators
• Upgrade to syn/quote/proc_macro2 version 1.0

Thanks to @kazimuth and @bardiharborow for additional internal improvements.

Commits

• 1f431c7 Remove obsolete CI badges
• d89758c Bump version numbers to 0.9.0
• ca6c72e Export shared crate root as module
• 3b8bf97 Make dependencies optional where possible
• f4f82b7 Modernize and simplify imports
• 6360ea5 Add new templates
• 0f90ab8 Improve spacing
• 5c4896a Add test for let declarations in blocks
• e69b761 Flush buffer before exiting block with non-empty scope (fixes #227)
• 8cc2048 Write conditional blocks before popping variable stack (see #227)
• Additional commits viewable in compare view

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