[Python Automation] Pin tsp-client version in pipeline script

User reported a dependency resolution issue when running `tsp-client init` command in the SDK generation pipeline.

Detailed errors:
```powershell
10:26:19.126 cmdout   [.Net] npx --package=@azure-tools/typespec-client-generator-cli --yes tsp-client init --tsp-config /mnt/vss/_work/1/s/azure-rest-api-specs/specification/storagediscovery/Microsoft.StorageDiscovery.Management/tspconfig.yaml --repo Azure/azure-rest-api-specs --commit 438273865aa78fed3838edab8f850a6624eb7227 --local-spec-repo /mnt/vss/_work/1/s/azure-rest-api-specs/specification/storagediscovery/Microsoft.StorageDiscovery.Management
10:26:24.903 cmderr   [.Net] npm warn ERESOLVE overriding peer dependency
10:26:24.904 cmderr   [.Net] npm warn While resolving: @azure-tools/typespec-client-generator-core@0.58.0
10:26:24.904 cmderr   [.Net] npm warn Found: @typespec/sse@undefined
10:26:24.904 cmderr   [.Net] npm warn node_modules/@typespec/sse
10:26:24.904 cmderr   [.Net] npm warn
10:26:24.904 cmderr   [.Net] npm warn Could not resolve dependency:
10:26:24.905 cmderr   [.Net] npm warn peer @typespec/sse@"^0.72.0" from @azure-tools/typespec-client-generator-core@0.58.0
10:26:24.905 cmderr   [.Net] npm warn node_modules/@azure-tools/typespec-client-generator-core
10:26:24.905 cmderr   [.Net] npm warn peer @azure-tools/typespec-client-generator-core@"^0.58.0" from @azure-tools/typespec-autorest@0.58.0
10:26:24.905 cmderr   [.Net] npm warn node_modules/@azure-tools/typespec-autorest
10:26:26.975 cmderr   [.Net] npm error code ETARGET
10:26:26.975 cmderr   [.Net] npm error notarget No matching version found for @typespec/sse@^0.72.0.
10:26:26.976 cmderr   [.Net] npm error notarget In most cases you or one of your dependencies are requesting
10:26:26.976 cmderr   [.Net] npm error notarget a package version that doesn't exist.
10:26:26.976 cmderr   [.Net] npm notice
10:26:26.977 cmderr   [.Net] npm notice New major version of npm available! 10.9.2 -> 11.4.2
10:26:26.977 cmderr   [.Net] npm notice Changelog: https://github.com/npm/cli/releases/tag/v11.4.2
10:26:26.977 cmderr   [.Net] npm notice To update run: npm install -g npm@11.4.2
10:26:26.977 cmderr   [.Net] npm notice
10:26:26.977 cmderr   [.Net] npm error A complete log of this run can be found in: /home/cloudtest/.npm/_logs/2025-07-15T22_26_19_202Z-debug-0.log
```
The root cause is one of the typespec library package failed to publish but others succeeded.

@msyyc
To avoid the impact to the end users which uses the `tsp-client`, it would be better for each language script to pin the `tsp-client` version instead of using the latest version. The version can be updated after the validation succeeds.

CC: @mikeharder @catalinaperalta