Fix main_build.yml (#61)

Main build is failing with: `Error: The version '3.1' with architecture
'x64' was not found for Ubuntu 22.04.` - I suspect this is because it's
treating 3.10 as a number (3.1) rather than a string ("3.10").

Failure:
https://github.com/aws-observability/aws-otel-python-instrumentation/actions/runs/7911600232/job/21596008343

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Author: thpierce

.github/workflows/main_build.yml

@@ -54,7 +54,7 @@ jobs:
           snapshot-ecr-role: ${{ secrets.AWS_ASSUME_ROLE_ARN }}
           push_image: true
           load_image: false
-          python_version: 3.10
+          python_version: "3.10"
           package_name: aws-opentelemetry-distro
           os: ubuntu-latest
 
@@ -82,4 +82,4 @@ jobs:
           pip install pytest
           pytest contract-tests/tests
 
-#  TODO: Add E2E tests
+#  TODO: Add E2E tests