saltclass error when expanding pillar value that is not of type 'str'

Description of Issue

When using saltclass for pillar data, variable expansion/interpolation fails when referenced pillar value is not a string. This does not appear to be an issue when simply referencing non-string pillar data within states, only when doing interpolation within saltclass itself.

Using the example below, referencing defaults:default_service_port in a state works fine. Interpolating as the value for myservice:port fails with the following exception shown in the master log: [salt.pillar :1218][CRITICAL][22870] Pillar render error: Failed to load ext_pillar saltclass: replace() argument 2 must be str, not int

This appears to be coming from salt.utils.saltclass in find_and_process_re() and/or find_value_to_expand(). The call to str.replace() in find_and_process_re() fails because find_value_to_expand() returns expanded pillar data in its original type, and str.replace() needs its second argument to be a string, as the log entry states.

Setup

Example pillar data

pillar:
  defaults:
    default_service_port: 1234
  myservice:
    port: ${defaults:default_service_port}

Steps to Reproduce Issue

1. Call salt <target> pillar.get defaults:default_service_port. This should return 1234 correctly.
2. Call salt <target> pillar.get myservice:port, salt <target> pillar.items, or anything else that would make the interpolation attempt occur. The only log entry Salt provides that I have seen is [salt.pillar :1218][CRITICAL][22870] Pillar render error: Failed to load ext_pillar saltclass: replace() argument 2 must be str, not int, but more details can be seen with pdb.

Versions Report

Salt Version:
          Salt: 3003.4

Dependency Versions:
          cffi: 1.14.0
      cherrypy: Not Installed
      dateutil: 2.8.1
     docker-py: Not Installed
         gitdb: Not Installed
     gitpython: Not Installed
        Jinja2: 2.11.1
       libgit2: 0.28.4
      M2Crypto: 0.35.2
          Mako: Not Installed
       msgpack: 0.6.2
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     pycparser: 2.20
      pycrypto: 2.6.1
  pycryptodome: 3.13.0
        pygit2: 1.0.3
        Python: 3.6.8 (default, Nov 16 2020, 16:55:22)
  python-gnupg: Not Installed
        PyYAML: 5.3
         PyZMQ: 17.0.0
         smmap: Not Installed
       timelib: Not Installed
       Tornado: 4.5.3
           ZMQ: 4.1.4

Salt Extensions:
        sseape: 8.6.0.3

System Versions:
          dist: centos 7 Core
        locale: UTF-8
       machine: x86_64
       release: 3.10.0-1160.59.1.el7.x86_64
        system: Linux
       version: CentOS Linux 7 Core

Start in salt/utils/saltclass.py, focusing on find_and_process_re() and find_value_to_expand(), then reproduce the example with a numeric defaults:default_service_port value. Confirm that pillar.get myservice:port and pillar.items complete without the reported replace() type error while direct access to the numeric value still works.