develop: sentence-case the "technical resources" headings

Vale (Temporal.Headings) requires sentence-style capitalization; the Java
and TypeScript dev guide pages already comply, but the .NET, PHP, Python,
Ruby, and Rust pages title-case the heading. Sentence-case all five for
consistency. Heading slugs are unchanged (Docusaurus lowercases them) and
nothing links to these anchors.

Author: DABH

docs/develop/dotnet/index.mdx

@@ -86,7 +86,7 @@ From there, you can dive deeper into any of the Temporal primitives to start bui
 - [Debugging](/develop/dotnet/best-practices/debugging)
 - [Converters and encryption](/develop/dotnet/best-practices/converters-and-encryption)
 
-## Temporal .NET Technical Resources
+## Temporal .NET technical resources
 
 - [.NET Quickstart](/develop/dotnet/set-up-your-local-dotnet)
 - [.NET API Documentation](https://dotnet.temporal.io/api/)

docs/develop/php/index.mdx

@@ -72,7 +72,7 @@ From there, you can dive deeper into any of the Temporal primitives to start bui
 - [Testing](/develop/php/best-practices/testing-suite)
 - [Debugging](/develop/php/best-practices/debugging)
 
-## Temporal PHP Technical Resources
+## Temporal PHP technical resources
 
 - [PHP SDK Quickstart - Setup Guide](/develop/php/set-up-your-local-php)
 - [PHP API Documentation](https://php.temporal.io)

docs/develop/python/index.mdx

@@ -96,7 +96,7 @@ From there, you can dive deeper into any of the Temporal primitives to start bui
 - [Strands Agents integration](/develop/python/integrations/strands-agents)
 - [Tenuo integration](https://tenuo.ai/temporal)
 
-## Temporal Python Technical Resources
+## Temporal Python technical resources
 
 - [Python SDK Quickstart - Setup Guide](/develop/python/set-up-your-local-python)
 - [Python API Documentation](https://python.temporal.io)

docs/develop/ruby/index.mdx

@@ -88,7 +88,7 @@ From there, you can dive deeper into any of the Temporal primitives to start bui
 - [Debugging](/develop/ruby/best-practices/debugging)
 - [Converters and encryption](/develop/ruby/best-practices/converters-and-encryption)
 
-## Temporal Ruby Technical Resources
+## Temporal Ruby technical resources
 
 - [Ruby SDK Quickstart - Setup Guide](/develop/ruby/set-up-local-ruby)
 - [Ruby SDK Code Samples](https://github.com/temporalio/samples-ruby)

docs/develop/rust/index.mdx

@@ -59,7 +59,7 @@ Once your local Temporal Service is set up, continue building with the following
 
 - [Feature guide](/develop/rust/nexus/feature-guide)
 
-## Temporal Rust Technical Resources
+## Temporal Rust technical resources
 
 - [Rust SDK Quickstart - Setup Guide](/develop/rust/quickstart)
 - [Rust API Documentation](https://docs.rs/temporalio-sdk/latest/temporalio_sdk/)