Use caret (semver bounds) for matrix.org packages

See https://python-poetry.org/docs/dependency-specification/#caret-requirements

This effectively:
- imposes new constraints `canonicaljson < 2` and `signedjson < 2`
- widens `1.2.1 <= matrix-common < 1.3` to `1.2.1 <= matrix-common < 2`

Doing so helps give us room to make backwards-compatible changes to our
libraries without screwing over old synapse versions installed with the
latest dependencies.

pyproject.toml

@@ -110,9 +110,9 @@ jsonschema = ">=3.0.0"
 frozendict = ">=1,!=2.1.2"
 # We require 2.1.0 or higher for type hints. Previous guard was >= 1.1.0
 unpaddedbase64 = ">=2.1.0"
-canonicaljson = ">=1.4.0"
+canonicaljson = "^1.4.0"
 # we use the type definitions added in signedjson 1.1.
-signedjson = ">=1.1.0"
+signedjson = "^1.1.0"
 # validating SSL certs for IP addresses requires service_identity 18.1.
 service-identity = ">=18.1.0"
 # Twisted 18.9 introduces some logger improvements that the structured
@@ -150,7 +150,7 @@ typing-extensions = ">=3.10.0.1"
 cryptography = ">=3.4.7"
 # ijson 3.1.4 fixes a bug with "." in property names
 ijson = ">=3.1.4"
-matrix-common = "~=1.2.1"
+matrix-common = "^1.2.1"
 # We need packaging.requirements.Requirement, added in 16.1.
 packaging = ">=16.1"
 # At the time of writing, we only use functions from the version `importlib.metadata`