Improve CallableType join in simple cases

[hauntsaninja]

Fixes #17479 , although as you can see in the test case the logic still remains far from perfect

[hauntsaninja]

ddtrace:
fixes false positive in utils_redis.py
schema is because we have a nested dict, so inferring narrower types on the inner dicts means the outer dict becomes dict[str, object] instead of dict[str, dict[str, builtins.function]]
span_attribute_schema seems regrettable, let me see what i can do

prefect:
fixes false positive in profile.py
it's unclear to me how provisioners was working earlier, was it inferring a union? will look further

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/cli/profile.py:180: error: Cannot call function of unknown type  [operator]

dd-trace-py (https://github.com/DataDog/dd-trace-py)
+ ddtrace/internal/schema/__init__.py:43: error: Value of type "object" is not indexable  [index]
+ ddtrace/internal/schema/__init__.py:44: error: Value of type "object" is not indexable  [index]
+ ddtrace/internal/schema/__init__.py:45: error: Value of type "object" is not indexable  [index]
+ ddtrace/internal/schema/__init__.py:46: error: Value of type "object" is not indexable  [index]
+ ddtrace/internal/schema/__init__.py:47: error: Value of type "object" is not indexable  [index]
+ ddtrace/internal/schema/__init__.py:48: error: Value of type "object" is not indexable  [index]
+ ddtrace/internal/schema/__init__.py:49: error: Value of type "object" is not indexable  [index]
+ ddtrace/internal/schema/__init__.py:50: error: Value of type "object" is not indexable  [index]
+ ddtrace/_trace/utils_valkey.py:35: error: Unused "type: ignore" comment  [unused-ignore]

[hauntsaninja]

Fixed some stuff, this looks good now. Fixes two false positives. Better inference leads to one new false positive, but really it should have an annotation and it will make subsequent inference for calls better